| Three years ago, researchers announced the discovery
of human genes that were capable of turning ordinary cells into malignant ones.
The news met with some skepticism. Experts asked how a single gene could cause
such a dramatic change. Why does cancer take years or even decades to develop if
it is caused by such a simple and direct process In last week’s issue of the,
three research teams answered those questions by setting forth a new model for
understanding the role of oncogenes in cancer. Each group found that it does in fact take more than a single gene to produce cancer in normal cells. Teams at M. I. T and Cold Spring Harbor Laboratory on Long Island, N. Y. , reported that they could induce cancer in normal rat cells only by inserting at least two types of oncogene into the cells. "A single oncogene produced some changes, A. was caused by normal cells B. sometimes resulted from internal actions of the victim’s own body C. was a hereditary disease D. was a form of malignancy [单项选择]A. Three years ago. B. For three years.
C. Maybe in three years. D. No, only three years. [填空题]His brother joined the army three years ago.
His brother______ ______ ______the army for three years.
[单项选择]College librarian: Until three years ago, nonstudents used the library without charge. Then, because of our decreased budget, they were asked to pay $100 per year. Nevertheless, about 150 nonstudents still use the library without paying. We will therefore gain financially if we hire a guard to identify nonstudents and ensure that they have paid the fee.
Which of the following would it be most important to know in order to evaluate the librarian’s conclusion A. The number of students who use the library annually. B. The library’s budget this year. C. Whether the library has installed an expensive computerized cataloging system. D. How much the library’s budget was decreased three years ago. E. (E) The annual cost to the library of hiring a guard. [单项选择]
Why did Ms. Mann go to Argentina three years ago A. She went to see her grandparents. B. She went for pleasure. C. She wrote political reports for the BBC. D. She wrote economic stories for the BBC. [填空题]His brother joined the army three years ago.
His brother______ ______ ______the army for three years. [单项选择]Carl studied in our high school three years ago. Last August his father found a job in another city and his family moved there. He began to study in a new school and we often write to each other. He often tells me something about the city where he lives now and his studies in the school. So I can know what happens to him.
Last Friday Carl came to our city again. He hoped to stay with his old grandpa during the summer holiday. He’s taller and stronger than before. We swam in the river outside the city together or had a picnic on the island. It surprised me that he has learned to cook when we were travelling in the wild forest. He told me his parents were both busy and sometimes he stayed at home alone and he had to look after himself. "How do you like your school" I asked. "Wonderful," said the young man. "It has a tall building and there’re two chemistry labs, two biology labs and three physics ones. And our library is big and there’re plenty of books in it." "I can A. take his summer vacation B. look after his grandpa C. swim in the river D. know what happens [填空题]Ms Clark came to Beijing three years ago．
→It has been______． 我来回答: 提交
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