用所给单词的适当形式填空。
—________ your father __________(fly) abroad yet?
—Yes, he has been in Singapore for a week.
The men were clearing all the _____________(pollute) from the lake.
Xuzhou is one of the __________(north) cities in Jiangsu.
My brother__________(buy) some storybooks foe me just now. I like them very much.
Let’s use the computer __________(help) us do the homework..