—Could you please tell me ______? 

— Sorry, I don't know, either. [ ]

A. what the matter is with him

B. where they will go for their holiday

C. that he has gone to Beijing

D. how long can the book be kept

在使用保鲜膜为食物保鲜时，最好选用（）薄膜。因为这种材料不含增塑剂，使用起来相对安全一些。

A、聚乙烯

B、聚氯乙烯

C、聚丙烯