The child asked his mother ______ go out to play tennis.

A．that he could

B．if he could

C．if could he

D．that could he

制备单价特异性抗血清时，去除杂抗体的方法是（）。

A.凝胶过滤法

B.亲和层析法

C.离子交换层析法

D.流式细胞术

E.酶解法