读一读，写一写。

Zip: Which season do you like best?

Zoom: I like autumn best.

Zip: Do you like summer?

Zoom: No, I don't. It's too hot.

Zip: Why do you like autumn, Zoom?

Zoom: Because I can pick fresh apples. And I can eat a lot. The colours are beautiful, too. What about you, Zip?

Zip: I like summer best. I like swimming.

Zip and Zoom are good friends. Zip likes____ best. Because she likes____. Zoom likes____ best.

Because he can ____. And he can eat a lot, too. He doesn't like summer. Because it is too____.

写出下列粒子的电子式：

（1）Na₂O_{2 ____}（2）氮原子　 ____（3）Na₂S ____（4）H₂O ____

一个自然数的七进制表达式是一个三位数，而这个自然数的九进制表达式也是一个三位数，而且这两个三位数的数码顺序恰好相反．则这个自然数是____ ．