题目

A child who has once been pleased with a tale likes, as a rule, to have it retold in almost the same words, but this should not lead parents to treat printed fairy stories as formal texts. It is always much better to tell a story than read it out of a book, and, if a parent can produce what, in the actual situation of the time and the child, is an improvement on the printed text, so much the better.     A charge made against fairy tales is that they harm the child by frightening him or making him sad thinking. To prove the latter, one would have to show in a controlled experiment tha下列与遗传变异有关的叙述，正确的是： A．三倍体西瓜不能形成正常的配子，是因为秋水仙素能抑制纺锤体的形成 B．若DNA中某碱基对改变，其控制合成的蛋白质分子结构可能不变 C．体内DNA复制时，双链完全解开，复制反向进行，不需要引物和DNA连接酶 D．基因重组可以通过产生新的基因，表现出性状的重新组合