设计阶段尽量随机选择研究对象，在多个医院选择对象等方法以减少的偏倚是

A．回忆偏倚

B．奈曼偏倚

C．Berkson偏倚

D．暴露偏倚

E．混杂偏倚

Those who ____ in ____ compositions, please hand them in this afternoon. [ ]

A. hasn't handed; his

B. haven't handed; their

C. has handed; their

D. have handed; his