— 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

当光线与平面镜成90°射向镜面时，此光线的反射角为______；若入射光线不动，镜面绕入射点转过30°，那么，此时反射光线与入射光线的夹角为______．