As soon as the manager entered his office, he began to_____the telephone book on his desk.

A．look up

B．look into

C．look upon

D．look through

在随机对照试验中，控制选择性偏倚的方法（）

A.严格掌握研究对象的人选标准

B.采用随机分组的方法

C.仪器和试剂标准化

D.使用盲法

E.采用随机抽样的方法