病例对照研究属于哪一种流行病学研究方法（）

A.描述流行病学

B.分析流行病学

C.实验流行病学

D.理论流行病学

E.以上均不对

—Is there anything wrong with you, Jake? You look so pale．

—I feel very tired．I _____on this boring paper every day so far this month．

A．work

B．have been working

C．had been working

D．am working