题目

人类常染色体上珠蛋白基因（A+）既有显性突变（A）又有隐性突变（a），突变均可导致地中海贫血。一对皆患地中海贫血的夫妻生下了一个正常的孩子，这对夫妻可能A.都是纯合子 B.都携带隐性突变基因 C.都是杂合子 D.都不携带显性突变基因 答案：【答案】C【解析】由题意可知正常孩子的基因型是A+A+，而这对夫妇都是地中海贫血的患者，基因型可能是A A+，A+a，但肯定都是杂合子，C正确，A、B、D错误。Can you imagine a classroom without one thing that has long been considered a necessary part? No notebooks, no textbooks, no test papers. Nor are there any pencils or pens, which always seem to run out of ink at the critical moment. A “Paperless classroom” is what more and more schools are trying to realize. Students don’t do any handwriting in this class. Instead, they use hand-sized or specially-designed computers. The teacher downloads texts from Internet libraries and sends them to every student’s personal computer. Having computers also means that students can use the Web. They can look up information on any subject they’re studying, from maths to social science. A high school teacher, Judy Herrel in Florida, US, described how her class used the Web. “Using a book that’s three or four years old is impossible,” she said. A paperless classroom is a big step towards reducing the waste of paper. “Think about the money and trees we could save with the computers,” she said. But, with all this technology, there’s always a risk that the machines will break down. So, in case of a power failure or a technical problem, paper textbooks should still be widely available (可得到的) for these students. 1.The underlined word “critical” in the first paragraph probably has the same meaning as _______. A. worrying            B. dangerous        C. happy          D. important 2.You are sure to find __________ in a paperless classroom. A. pens                B. computers        C. test papers    D. notebooks 3.According to Judy Herrel, __________. A. the Web can talk the students everywhere B. the Web can take the place of teachers C. the Web is a better tool for information D. the Web is for downloading information 4.The paper textbooks should still be widely available because __________. A. students won’t have trouble with their pens B. computers may break down sometimes C. students may not get all information from the Internet D. paper textbooks may give students more information