单选题The detective and his assistant have begun to _____ the mysterious murder.

单选题Mr. Green said his clients ______ our samples by the end of last month.

单选题Would you please bring me some ______ catalogues? These are too old.

单选题A: We should write letters to our friends who live outside the country. B: ______.

单选题Customer: ______ Clerk: Here you are. 20 dollars. A. Give me 20 dollars worth of stamps, please. B. I want to purchase 20 dollars of stamps, please. C. Five 2-dollar and ten 1-dollar stamps, please. D. Could I have some stamps, please?

单选题阅读下列短文，然后根据短文的内容从每小题的四个选择项中选出最佳的一项。B　　Maria Mitchell（1818-1889）,the first woman asdivonomer（天文学家）in the United was born in Nantucket, Massachusetts.Her parents valued education and insisted on giving

单选题"Will you be able to finish the job this week?" " ______." A. I can't say it B. I don't know that C. I'm not sure this D. I don't expect so

单选题I made this myself but it was ______ who taught me.

单选题_______rooms are both large and comfortable.

单选题Many of the tech industry"s biggest companies, like Amazon, Google, IBM and Microsoft, are jockeying to become the leader for artificial intelligence (A.I.). In the industry"s term, the companies are engaged in a "platform war." A platform, in technology, is essentially a piece of software that other companies build on and that consumers cannot do without. Become the platform and huge profits will follow. Microsoft dominated personal computers because its Windows software became the center of the consumer software world. Google has come to dominate the Internet through its ubiquitous search bar. If true believers in A.I. are correct that this long-promised technology is ready for the mainstream, the company that controls A.I. could steer the tech industry for years to come. "Whoever wins this race will dominate the next stage of the information age," said Pedro Domingos, a machine learning specialist and the author of "The Master Algorithm," a 2015 book that contends that A.I. and big-data technology will remake the world. In this fight—no doubt in its early stages—the big tech companies are engaged in tit-for-tat publicity stunts, circling the same start-ups that could provide the technology pieces they are missing and, perhaps most important, trying to hire the same brains. Fei-Fei Li, a Stanford University professor who is an expert in computer vision, said one of her Ph.D. candidates had an offer for a job paying more than $1 million a year, and that was only one of four from big and small companies. For years, tech companies have used man-versus-machine competitions to show they are making progress on A.I. In 1997, an IBM computer beat the chess champion Garry Kasparov. Five years ago, IBM went even further when its Watson system won a three-day match on the television trivia show "Jeopardy!" Today, Watson is the centerpiece of IBM"s A.I. efforts. By 2020, the market for machine learning applications will reach $40 billion, IDC, a market research firm, estimates. And 60 percent of those applications, the firm predicts, will run on the platform software of four companies—Amazon, Google, IBM and Microsoft. Intelligent software applications will become commonplace, said Jeff Dean, a computer scientist who oversees Google"s A.I. development. "And machine learning will touch every industry."

单选题Fear and its companion pain are two of the most useful things that men and animals possess, if they are properly used. If fire did not hurt when it burnt, children would play it until their hands were burnt away. Similarly, if pain existed but fear did not, a child would burn itself again and again, because fear would not warn it to keep away from the fire that had burn it before. A really fearless soldier--and some do exist--is not a good soldier because he is soon killed; and a dead soldier is of no use to his army. Fear and pain are therefore two guards without which men and animals might soon die out. In our first sentence we suggested that fear ought to be properly used. If, for example, you never go out of your house because of the danger of being knocked down and killed in the street by a car, you are letting fear rule you too much. Even in your house you are not absolutely safe: an airplane may crash on your house, or ants may eat away some of the beams in your roof so that the latter falls on you, or you may get cancer! The important thing is not to let fear rule you, but instead to use fear as your servant and guide. Fear will warn you of dangers; then you have to decide what action to take. In many cases, you can take quick and successful action to avoid the danger. For example, you see a car coming straight towards you; fear warns you, you jump out of the way, and all is well. In some cases, however, you decide that there is nothing that you can do to avoid the danger. For example, you cannot prevent an airplane crashing onto your house. In this case, fear has given you its warning; you have examined it and decided on your course, of action, so fear of this particular danger is no longer of any use to you, and you have to try to overcome it.

单选题The scientists at the University of Bern in Switzerland have used a weakened virus that is not infectious and has proved safe and effective.

单选题The organization had broken no rules, but ______ had it acted responsibly.

单选题______ is generally believed, there is no water on the moon.

单选题It is not ______ to discuss the question again and again.

单选题Contradictory to popular belief, recent surveys show that besides housewives, many college students are also ______ to soap operas.

单选题Gaining a new customer costs ______ keeping an old one.

单选题A century ago the physician's word was______: to doubt it was considered almost sacrilegious.