九年级上册英语句子后面可以添加不同的结构来丰富句子的表达和含义。以下是一些常见的句子后面可以添加的结构：

疑问句

What/How about + doing sth.？

Why don't you + do sth.？

Why not + do sth.？

Shall we/I + do sth.？

祈使句

Let's + do sth.

否定句

I'm too tired to say anything.

She can't come to the phone right now.

比较句

One of the liveliest cities in the world is New York.

She sings better than her sister.

条件句

If I had known about the party, I would have attended it.

Unless it rains, we will go hiking tomorrow.

建议句

You could try calling her again.

Why not give it a try？

感叹句

What a beautiful day it is!

How lucky you are to have such a great family!

这些结构可以帮助你更灵活地表达不同的意思，使你的英语表达更加丰富和地道。建议你在日常学习和练习中多使用这些结构，以提高自己的英语水平。