There isn’t_____airport near where I live. _____ nearest one is 110 kilometers away.

A．an; The

B．the; The

C．an; A

D．an; An

病例对照研究中采用分层分析可以控制（）

A.入院率偏倚

B.现患病例-存活病例偏倚

C.混杂偏倚

D.回忆偏倚

E.信息偏倚