就病例对照研究而言,下述哪项是正确的()
A.属于分析性研究
B.计算RR
C.研究方向由因及果
D.不适用于对罕见病的研究
E.能直接计算得到发病率
参考答案:A
I ______ for Shanghai this Saturday, so I want to know when the earliest plane ______.
A.leave; takes off
B.am leaving; takes off
C.leave; is taking off
D.am leaving; is taking off