单选题You can tell age of a tree by counting its rings. But these records of a tree's life really say a lot more. Scientists are using tree rings to learn what's been happening on the sun's surface for the last ten thousand years. Each ring represents a year of growth. As the tree grows, it adds a layer to its trunk, taking up chemical elements from the air. By looking at elements in the rings from a certain year, scientists can what elements were in the air that year. Dr. Stevenson is analyzing one element, carbon-14, in rings from both living and dead trees. Some rings go back almost ten thousand years to the end of the Ice Age. When Stevenson followed the carbon-14 track back in time, he found carbon-14 levels changed with the intensity of solar buring. You see, the sun has cycles. Sometimes it burns fiercely, and at other times it's relatively calm. During the sun's violent periods, it throws off charged formation of carbon-14 on earth. When there is more solar wind activity, less carbon-14 is produced. Ten thousand years of tree rings show that the carbon-14 level rises and falls about every 420 years. The scientists concluded that solar wind activity must follow the same cycle.

单选题The rebels ______ the government and declared their independence from its rule.

单选题The opening ceremony is a great occasion. It is essential ______ for that. A. for us to be prepared B. that we are prepared C. of us to be prepared D. our being prepared

单选题No sooner had Tom seen Jim ______ he left the room.

单选题Some women ______ a good salary in a job instead of staying home, but they decided not to work for the sake of the family.

单选题The road is laid ahead of him, a ______ gray line stretching to the horizon.

单选题_____ idea of _____ sounds much better than Clare`s.

单选题______ : An error can be caused by attempting to divide by 0. A．Interrupt B．Default C．Underflow D．Overflow

单选题______ sugar ______ salt is oil water.

单选题The exam was ______easier than we had expected.

单选题Mr. Smith ______ working till he was seventy years old.

单选题We can learn from the passage that______. 

单选题The most important ______ of his speech was that we Should all work whole-heartedly for the people.

单选题He knows little of English to say( )of English culture.

单选题Which of the following is the least desirable to a journalist according to the author?

单选题They are both very determined people, so there's rather ______ by personalities.

单选题It demands artistic skill for a manager to ______ disputes among his employees. A. rectify B. rebuke C. negotiate D. reconcile

单选题As a matter of fact, the true nature of communication process can be concluded in one sentence: Who says ______ through what channel to whom.

单选题According to studies cited by the National Eating Disorders Association, 42 percent of girls in first through third grade want to be thinner, 81 percent of 10-year-olds are afraid of being fat, and 51 percent of 9-and 10-year-old girls feel better about themselves if they are on a diet. In many ,ways, this fixation on weight at ever earlier ages comes at an inopportune time physiologically. At a recent Hadassah meeting at the Woodlands Community Temple in White Plains, Dr. Maxcie Schneider, the director of adolescent medicine at Greenwich Hospital, and Erica Leon, a registered dietitian, spoke about early adolescence as a time when a little bit of pudginess is necessary for proper growth, and youngsters wrestle constantly with their body image. "I can't tell you how many kids I've seen who've been on the Atkins diet, or on the South Beach diet," Ms. Leon said, adding that overweight children who try diets can be at risk of developing eating disorders. After the presentation, three mothers from Hartsdale who wanted to help their children avoid such issues spoke about how their young daughters are already beginning to become weight-conscious. Anorexia is a mental illness in which the victim eats barely enough to survive, because her distorted thinking makes her think she is fat. Bulimia, a mental illness in which someone binges on large amounts of food, then purges it through vomiting or the abuse of laxatives, is on the rise, and is surfacing in younger and younger patients, mostly girls, said Judy Scheel, the director of the Center for Eating Disorder Recovery in Mount Kisco. About 90 percent of victims of eating disorders are female, and often the male victims are on teams like wrestling and crew, where they must keep their weight low for competitive reasons. Dr. Scheel believes that where girls claim the eating disorder enables them to be thin, boys typically state their goal is to achieve or maintain a muscular but thin physique. The average onset for bulimia used to be 17, but to see teenagers age 14 and 15 with bulimia is common these days, Dr. Scheel said. Other people believe the disorders have genetic or chemical components, and many people with eating disorders respond well to anti-depressants, for example. "A certain amount of education is necessary to help young people avoid becoming obsessed with their body image. Teachers need to stay outside of talking about diets," Dr. Scheel said. "It's like a parent, always talking about their next diet. You have to help a child understand that if you cat healthily and exercise, your body is going to take care of itself." And in relatively homogenous populations, like in some Westchester schools, competition runs high. "So the young people don't really see how beautiful diversity is," she said, "and they tend to all be competing for kind of the same goals./