—Did Alan see his old friends yesterday? —Yes, he did. He his old friends for several years.
________ plastic bags we use, ________ it will be to the environment.
Noise pollution can cause people to become sick. So our government has done________to stop it.
He _______ his head to see the _______ sun.
-These farmers have been to the United States. -Really? When _______ there?
The weather in Beijing is cooler than _______ in Guangzhou.