题目

下面对DNA的结构的叙述中，不正确的是 A．DNA分子中的脱氧核糖和磷酸交替连结，排列在外侧 B．DNA分子中的嘌呤碱基与嘧啶碱基总数相同 C．DNA分子中只有四种碱基，故实际上只能构成44种DNA D．DNA分子中碱基之间一一对应配对的关系是碱基互补配对原则 答案：C 　　Mother dog has five children. She likes them very much. One day, the mother dog goes out. Her children come to the side of the river to play. A big crocodile（鳄鱼）swims and sees the little dogs. He wants to eat them. He lies（躺）on the side of the river. The little dogs think he's a bridge（桥）. They climb up the bridge happily. The youngest dog can't climb up, so he has to stand and look at the bridge. Suddenly （忽然地）, the crocodile opens his mouth and eats the four dogs. The youngest dog runs away at once. He runs back home. Mother dog has come back. She is looking for her babies. The youngest dog cries, “Mum, come with, go to the bridge!” They run to the river. “Mum, my brothers and sisters are in the bridge,” says the youngest dog. Mother dog knows it's a crocodile, not a bridge. She goes home for a knife. She cuts the crocodile and the four little dogs jump out. They are saved（得救）. (1) The crocodile eats ________ baby dogs. [　　] A．five B．four C．three (2) Where do the baby dogs go that day? [　　] A．To a street. B．To a river. C．To a house. (3) Who can't climb up the “bridge”. [　　] A．The oldest dog. B．Mother dog. C．The youngest dog. (4) What does Mother dog get after she sees the crocodile? [　　] A．A knife. B．A pen. C．A basket. (5) Which of the following is true? [　　] A．The four dogs are saved. B．Mother dog is saved. C．The crocodile is saved.