题目

测得某DNA片段含有碱基1600个，其中腺嘌呤占27.5%，问该DNA复制两次需要游离的鸟嘌呤脱氧核苷酸有多少个（   ） A.2520个        B.1480个       C.1080个          D.720个 答案：C完形填空阅读下面短文，从每小题A、B、C三个选项中，选出可以填入空白处的最佳选项，并将其字母标号填入题前的括号内。I still remember about ten years ago, when I was a teenager, my father and I were standing in line to buy tickets for the circus(马戏). Soon, there was only one ______ in front of us. There were eight young children in it. I guessed they were not rich. Their clothes were a little old, but they were clean. The children talked ______ with each other about the clowns(小丑)they would see. I was sure that they ______ went out. So it was clearly a very exciting day out for them. Their parents stood ______ them and watched them talking.The ticket lady asked ______ tickets the father wanted. He proudly answered, “Please give me eight children’s tickets and two adults’ tickets, so I ______ take all my family to the circus.” The ticket lady told him the price. The father kept ______ for a short time. Then, again he asked, “How much did you say?” Then the tickets lady ______ the price more loudly. He said nothing, but the ______ on his face clearly showed that he didn’t have enough money.When I was wondering what he would do, I saw a $20 note fall onto the ground from ______ father’s hand. Then he tapped(拍) the man and said, “Excuse me, sir, you dropped this.” The man saw the note ______ on the ground and understood my father was helping him. He picked up the money. His face turned red and replied with ______, “Thank you, sir, thank you. This really means a lot to my family. I will never _____ your kindness.”______ I didn’t go to the circus that night, I saw something really wonderful. I began to ______ my father because of what he had done. Sometimes to offer help to others wasn’t easy, but how to help others would be even more difficult sometimes.1.A. man B. child C. family2.A. quietly B. excitedly C. luckily3.A. seldom B. always C. ever4.A. against B. beside C. across5.A. how much B. how often C. how many6.A. can B. should C. must7.A. crazy B. silent C. bored8.A. reviewed B. produced C. repeated9.A. expression B. attention C. introduction10.A. his B. their C. my11.A. lie B. tie C. rush 12.A. illness B. sadness C. shyness13.A. request B. forget C. complete14.A. Although B. Because C. If15.A. guard B. admire C. suggest