①有一次____一个牧童说____来____咱们把这口老泉清理一下____再挖一口小井____好不好____

②____你喝吧____孩子们说____我们就是为了让人喝水才把井砌好的____

③____我为你们三个人的健康喝了三口____她微笑着说____

当你漫步在林间小路上时，你会感到空气特别的清新和湿润，这是绿色植物的什么作用改善了空气的质量（  ）

① How many books do you have?____     A. I bought a lot of books.

② What are the rabbits doing?____     B. They are onions.

③ Can you play the piano? ____     C. I have twenty books.

④ What did you do last Sunday? ____     D. They are jumping.

⑤ What are these?____     E. Yes, I can.

黄铁矿矿石的主要成分为二硫化亚铁（FeS₂），取一块质量为30克的黄铁矿矿石样品在氧气中完全灼烧后得到10克氧化铁（其中的铁全来自二硫化亚铁）同时生成二氧化硫。