题目

具有100个碱基对的一个DNA分子片段，内含60个腺嘌呤，如果连续复制2次，则需要游离的鸟嘌呤脱氧核苷酸多少个（    ） A. 60              B. 80                C. 120          D. 180 答案：C—He didn’t go to the lecture this morning, did he?— _____ ．Though he was not feeling very well．A．No, he didn’t B．Yes; he didC．No, he did D．Yes, he didn’t