Could it be in the classroom_____ we had a talk last night _____you left your keys? 

A．that; where

B．in which; where

C．where; that

D．where; in which

衡量某因素和某疾病间联系强度的最好指标是（）

A.总人群中疾病的发生率

B.暴露者中疾病的发生率

C.因素的流行率

D.相对危险度

E.特异危险度