下列哪种维生素能阻断N-亚硝基化合物的合成（）

A.维生素B₂

B.维生素C

C.维生素D

D.维生素A

E.维生素B₁

根据首字母及汉语提示，完成下列单词的拼写，使句意明确，语言通顺。

小题1:What do you like to do in your f______(空闲的) time?

小题2:I could hear her sweet v______ (噪音) from the next room.

小题3:Travelling by plane is expensive, but it s______ (节省) time.

小题4:Would you please make a shopping l________ (清单) for the picnic?

小题5:It's polite to k______ (敲) on the door before entering a room.