It has been proved          taking exercise regularly does good to one’s health.

A．whether

B．when

C．what

D．that

下列反射活动属于条件反射的是（　　）

A．狗吃到肉，分泌唾液

B．青梅入口，分泌唾液

C．看见糖果，分泌唾液

D．强光射眼，迅速闭眼