题目

Knowing how long the test would last, the students who finished ____ back and waited until the end of the exam. A. settle     B. settled    C. settling    D. to settle 答案：B 解析: 该题考查句子结构。学生易犯思维定势的错误而选C，其实who finished是定语从句，该处缺谓语动词。基因重组可应用于 A．诱变育种     B．人工诱导多倍体育种    C．杂交育种       D．单倍体育种