She often goes to help the old man and tries to look after him as ______ as

she can.       [ ]

A. well

B. possible

C. much

在体外放射分析中，应用PEG等物质进行化学分离或沉淀分离，该分离法的缺点是（）。

A.分离需要时间长

B.分离的试剂成本高

C.试剂的通用性不强

D.分离时要求条件高

E.特异性和分离效果较差