下列各组物质，按单质、化合物、混合物顺序排列正确的是 [ ]

A．氮气、空气、干冰

B．液态氧、纯碱、碘酒

C．生石灰、熟石灰、石灰石

D．水银、石墨、盐酸

根据下列句子及所给汉语注释，写出空缺处各单词的正确形式，每空只写一词。

小题1:Cindy told me it was her __________ (第二) time to visit China

小题2:Thanks to the government, we can spend _________ (少的) money on TVs and things like that.

小题3:What about reading aloud to practice   _____________ (发音)?

小题4:My parents always tell me the__________(重要性）of working hard.

小题5:Although it was expensive, we _____________(决定) to buy it.