People all around the world have been doing as much as they can ________the people in Afghanistan.

A．help　　

B．to help

C．helping　　

D．helped

物质在射线激发下将吸收的能量以可见光形式释放称为（）.

A.发射现象

B.荧光现象

C.感光现象

D.吸收现象

E.衰变现象