—Do you mind if I open the window?

—      . I feel a bit cold.

A．Go ahead

B．Of course not, it's not allowed here.

C．I'd rather you didn't

D．Why not?

流行病学上，通常用来表示病原体的致病力（）

A、续发率

B、临床显性感染病例占血清阳性人群的比例

C、病死率

D、重症病例占临床显性感染病例的比例