牛津上海版（深圳用）英语六年级上册Unit 12基础练（单选题）

____rivers, oceans, land and forest.

The rivers ____clean before, but now they _____dirty.

Trees are very important to us. They can ____.

We should work together to keep the Earth clean and ____.

We live ____the Earth.

Don't use the ____bags. We should keep the city clean.

We are going to ____the rubbish on the hill.

Now the Earth _____sick.

We should stop ____wild animals.

Smoke ________ cars and buses makes the air dirty.