根据句意和首字母写单词。

1. Look! That is the football f______________. We often play football on it.

2. My aunt and my uncle work in a school. They are t______________.

3. The twins often help us. They are h______________.

4. Look at the sign. It says, "You can't f______________ kites here."

5. Some oranges are o______________. Some are green.

下列各组中的物质相互转化时，不能通过一步反应实现的是（　　）

A．Ca（OH）₂→CaC0₃

B．NaOH→Na₂S0₄

C．C→C0₂

D．KCl→KCl0₃