单选题The opposite of adaptive divergence is an interesting and fairly common expression of evolution. Whereas related groups of organisms take on widely different characters in becoming adapted to unlike environments in the case of adaptive divergence. We find that Unrelated groups of organisms exhibit adaptive convergence when they spot similar modes of life or become suited for special sorts of environments. For example, invertebrate marine animals living firmly attached to the sea bottom or to some foreign object tend to develop a sub- cylindrical or conical form. This is illustrated by coral individuals, by many sponges, and even by the diminutive tubes of bryozoans. Adaptive convergence in taking this coral-like form is shown by some brachiopods and pelecypods that grew in fixed position. More readily appreciated is the streamlined fitness of most fishes for moving swiftly through water; they have no neck, the contour of the body is smoothly curved so as to give minimum resistance, and the chief propelling organ is a powerful tail fin. The fact that some fossil reptiles (ichthyosaurs) and modem mammals (whales, dolphins) are wholly fishlike in form is an expression of adaptive convergence, for these air-breathing reptiles and mammals, which are highly efficient swimmers, are not closely related to fishes. Unrelated or distantly related organisms that develop similarity of form are sometimes designated as homeomorphs (having same form).

单选题Not only ______ us light, but also it gives us heat

单选题They also want the police"s use of force kept in check , especially in poor neighborhoods where everyone is apt to be treated like a suspect.

单选题Which do you think is the best title (题目) for the passage?

单选题{{B}}Text 1{{/B}} Can computer viruses ever be a force for progress? In the wild west of the online world, the archetypal baddies are computer viruses and worms. These self-replicating programs are notorious for wreaking havoc in the systems of unwary users. But, as in the west, not all gunslingers wear black hats. Some virus writers wish their fellow users well, and have been spreading viruses that are designed to do good, not harm. Cheese Worm, which appeared a few weeks ago, attempts to fix computers that have been compromised by the Lion Worm. The Lion Worm is dangerous. It infects computers that use the Linux operating system, and creates multiple "backdoors" into the infected computer. It then e-mails information about these backdoors to people who wish to misuse that computer for nefarious purposes such as "denial of service" attacks on websites. (Such attacks bombard a site with so many simultaneous requests for access that it comes out with its hands up.) That might sound like a good thing. So might VBS. Noped. A @ mm. This virus, which arrives as an e-mail attachment, searches a user's hard drive for specific files which the (unknown) virus writer believes contain child pornography. If the virus finds any files on the proscribed list, it e-mails a copy of the file in question to a random recipient from a list of American government agencies, with an explanatory note. The notion of "good" viruses may sound novel; but, according to Vesselin Bontchev, a virus expert with Frisk Software International in Iceland, it is not. However, early attempts to create beneficial viruses—for example, programs that compressed or encrypted files without asking a user's permission—were resented, because they represented a loss of control over a user's computer, and a diversion of data-processing resources. Inoculating computers against infection sounds like a good idea, but fails because any unauthorised changes are suspicious. Cheese Worm, even though it is designed to help the user whose disk it ends up on, suffers from the same objection. And VBS. Noped. A @ mm, whatever social benefits its author might think it has, is not even meant to do that. If it works, it will harm the user rather than help him. It is little more than cyber-vigilantism. Appropriate to the wild west, perhaps, but if cyberspace is to be civilised, other solutions will have to be found.

单选题The speaker had to______in the middle of his speech because of shouts of protest from the audience.

单选题 In the world of management, employees are nonexempt or exempt, depending on whether they get paid for overtime or not.{{U}} (21) {{/U}}a creative scientist, like a creative artist, does not see his or her time. The very idea of a creative scientist{{U}} (22) {{/U}}out time sheets is ludicrous. Fascination in science cannot be turned on or off on{{U}} (23) {{/U}}The creative mind continues to wander{{U}} (24) {{/U}}the body eats, exercises, or sleeps. Interruptions in or out of the laboratory, the library, the office or the home study may{{U}} (25) {{/U}}a promising effort.{{U}} (26) {{/U}}the well-established practice of moonlighting. Do what you need to do to keep the wolf{{U}} (27) {{/U}}from the door, the world{{U}} (28) {{/U}}your thesis adviser, team leader, or laboratory director. Then use the rest of your time, perhaps at night or on the weekends, to do{{U}} (29) {{/U}}you really want to do. All of us who had done science know how to{{U}} (30) {{/U}}effectively. So many scientific books are prefaced by remarks such as "I thank my spouse, who tolerated my awful antics while this book was being written." I{{U}} (31) {{/U}}that some of the most creative results to come out of my laboratory were obtained by graduate students or postdoctoral assistants in the{{U}} (32) {{/U}}of my instructions or even{{U}} (33) {{/U}}against them. The creative mind has a vision. And vision,{{U}} (34) {{/U}}Jonathan Smith, is the art of seeing things{{U}} (35) {{/U}}. To try to explain a vision can get one into serious trouble, as Joan of Arc (圣女贞德) found out. It is better to moonlight until things become visible.

单选题 {{B}}Directions:{{/B}} Below is a summary of some of the main points of the passage. Read the summary and then select the best word or phrase from the box below according to the passage. You should decide on the best choice and mark the corresponding letter on the ANSWER SHEET with a single line through the center. A porridge H storage life B malnutrition I sprouted grains C fermentation J inadequate food intake D new technology K acidity E contaminated food L unfermented food F diarrhoeal germs M weaning G traditional food N dough Malnutrition and the resulting impaired growth and development in children of weaning age in developing countries results not only from{{U}} (18) {{/U}}but also from infections caused by contaminated food. Studies have addressed the problem of inadequate intake by using sprouted grains in food preparation. Contamination has been tackled with{{U}} (19) {{/U}}. Both of these methods are, or were, used traditionally and are practical and inexpensive. Fermented foods have higher{{U}} (20) {{/U}}and also have anti-microbial qualities. This means that contamination is decreased and that their{{U}} (21) {{/U}}is increased. Fermentation occurs when{{U}} (22) {{/U}}is left to stand, occasionally with simple additives. There is, however, a trend away from this{{U}} (23) {{/U}}to commercial products.

单选题While the total number of farmers engaged in agricultural production is barely half ______ it used to be in 1959, the size of the average farm has tripled. A. that B. what C. which D. how

单选题Symantec might not block

单选题The doctor suggests that a person ______ exercises every day if he wishes to be healthy.

单选题The words “good sense”( Par

单选题In 1993, I published a book, The Rage of a Privileged Class, whose central thesis was that even the most gifted African-Americans assumed that they would never crash through America's glass ceiling—no matter how talented, well educated, or hardworking they were. Few people of any race would claim that true equality has arrived; but so much has changed since Rage came out. Color is becoming less and less a burden; race is less and less an immovable barrier. My new research explores how that phenomenon is changing the way people of all races view the American landscape. I polled two groups of especially accomplished people of color. One is the African-American alumni of Harvard Business School. The other is the alumni of A Better Chance, a program, founded in 1963, that sends ambitious, talented youngsters to some of the nation's best secondary schools. Generations, I concluded from my study, mattered deeply—with their defining characteristics rooted in America's evolving racial dynamics. Generation 1, in this categorization, is the civil-rights generation—those (born before 1945) who participated in, or simply bore witness to, the defining 20th-century battle for racial equality. It is the generation of whites who, in large measure, saw blacks as alien beings and the generation of blacks who, for the most part, saw whites as irremediably prejudiced. Gen 2s (born between 1945 and 1969) were much less racially constrained—though they remained, in large measure, stuck in a tangle of racial stereotypes. Gen 3s (born between 1970 and 1995) saw race as less of a big deal. And that ability to see a person beyond color has cleared the way for a generation of Believers—blacks who fully accept that America means what it says when it promises to give them a shot. That new reality made itself clear when I compared black Gen 1 Harvard M. B. A. s with their Gen 3 counterparts. Seventy-five percent of Gen 1s said blacks faced "a lot" of discrimination, compared with 49 percent of Gen 3s. Twenty-five percent of Gen 1s thought their educational attainments put them "on an equal professional footing with white peers or competitors with comparable educational credentials," compared with 62 percent of Gen 3s. Ninety-three percent of Gen 1s saw a glass ceiling at their current workplaces, compared with 46 percent of Gen 3s. I am not about to make a statistical argument based on these numbers, but the message nonetheless seems clear. In the time since the Gen 1s came on the scene, a revolution has occurred. Those uptight suburbanites who couldn't imagine socializing with, working for, or marrying a "Negro," who thought blacks existed in an altogether different dimension, who could no more see dining with a black person than dining with a giraffe, have slowly given way to a new generation that embraces—at least consciously—the concept of equality. Americans have, in some substantial way, re-created each other—to an extent that our predecessors might find astounding.

单选题Unless we spend money to spot and prevent asteroids (小行星) now, one might crash into Earth and destroy life as we know it, say some scientists. Asteroids are bigger versions of the meteoroids (流星) that race across the night sky. Most orbit the sun far from Earth and don't threaten us. But there are also thousands whose orbits put them on a collision course with Earth. Buy $ 40 million worth of new telescopes right now. Then spend $10 million a year for the next 25 years to locate most of the space rocks. By the time we spot a fatal one, the scientists say, we'll have a way to change its course. Some scientists favor pushing asteroids off course with nuclear weapons. But the cost wouldn't be cheap. Is it worth it? Two things experts consider when judging any risk are: 1) How likely the event is; and 2) How bad the consequences if the event occurs. Experts think an asteroid big enough to destroy lots of life might strike Earth once every 400000 years. Sounds pretty rare—but if one did fall, it would be the end of the world. "If we don't take care of these big asteroids, they'll take care of us," says one scientist. "It's that simple. " The cure, though, might be worse than the disease. Do we really want fleets of nuclear weapons sitting around on Earth? "The world has less to fear from doomsday (毁灭性的) rocks than from a great nuclear fleet set against them," said a New York Times article.

单选题It was Sunday. The trains were crowded. A gentleman was walking along the (1) looking into the windows and trying to find a place. In one of the (2) he saw a vacant seat. But a small suitcase was lying on (3) and a stout gentleman was sitting next to it. " Is this seat vacant?" "No, it is my friend's," (4) the stout gentleman. "He is coming. This is his suitcase./

单选题Those days people throughout the world were looking forward to the day of victory with great ______.