When Tom got to the examination room, he realized he ______ his pen at home.

A．was leaving

B．had left

C．forgot

D．was forgetting

确定某暴露因素与某疾病联系的强度用（）

A.该人群中暴露于该因素的暴露率

B.相对危险度

C.该人群中该病的患病率

D.人群归因危险度

E.该人群中该病的发病率