下列哪种药物有可逆性卵巢切除的作用（）

A.GnRH类似物

B.大剂量孕激素

C.大剂量雌激素

D.大剂量雄激素

E.大剂量催乳素

I was giving a talk to a large group of people, the same talk I _______ to half a dozen other groups.

A．was giving

B．am giving

C．had given

D．have given