第31题: [单项选择]Girl sperm was preferred to boy sperm in the research most probably because ________. A. girl sperm contains more genetic material B. more mothers want to have girl babies C. girl sperm is healthier and more active D. girl sperm is more easily purified 参考答案:A 答案解析:[定位] 第1段倒数第二句。
[解析] 该句中的由which引导的定语从句表明选项A的叙述正确。
[点睛] 定语从句往往描述先行词的性质状态,值得注意。