Mike often got into trouble with others at school,but his teacher didn't ___trying to help him .           [ ]

A worry about  

B afford to  

C give up      

D pay attention to

镜面反射说法正确的是（）。

A.当界面大于波长时发生

B.当界面小于波长时发生

C.由于界面小于3mm而发生

D.与入射角无关

E.以上都不是