--- Did you catch the train to Beijing last night?

--- No. It ______ for ten minutes by the time I got to the station.

A．has left

B．had left

C．has been away

D．had been away

下面对流行病学应用叙述正确的是（）。

A.疾病预防和健康促进

B.疾病的监测

C.疾病病因和危险因素的研究

D.疾病的自然史

E.疾病预防的效果评价