Many people came to the meeting，but   them who left early was 35．

A．a number of

B．the number

C．a lot of

D．the number of

一项1:1配对病例对照研究有113对病例和对照，病例和对照均有暴露史的是69对，病例有暴露而对照无暴露史的是33对，对照有暴露而病例无暴露的是10对，其OR值为

A．0.21

B．0.30

C．3.3

D．16

E．4.78