— What else can we do?

—An international effort is required to cope with ____ urgent need of ____earthquake victims.

A．the;the

B．a;an

C．an;a

D．a;the

哺乳动物的次级卵母细胞只能存在于以下哪一结构中？（）

A.原始滤泡

B.初级滤泡

C.次级滤泡

D.三级滤泡