— Have you ever come here before?

— No, it is the first time that I______ to this city.

[      ]

A. have been

B. had been

C. came

D. come

某医师欲采用横断面调查研究的方法，调查高血压病在人群中的分布情况，选择最合适的指标为

A．病死率
B．发病率
C．死亡率
D．患病率
E．二代发病率