以下提供若干组考题，每组考题共同使用在考题前列出的A、B、C、D、E五个备选答案。请从中选择一个与问题关系最密切的答案。

X线的摄影是

A．穿透作用
B．荧光作用
C．电离作用
D．感光作用
E．生物效应

—Can you see                   ?

—No. Let’s go and have a look. Maybe we can help them.[ ]

A. what was happening there

B. what are they doing there

C. what are they talking there

D. what is happening there