We must keep them away from the wetland ________ protect the wildlife around here.

The unquestioned role of students is to learn as much as possible through ________ method they find.

A growing number of people prefer to shop online because the prices of the goods on the Internet are usually much lower than ______ in the malls.

Our teacher always gives us good advice. We should follow .

Please remember to _____ a stamp _____ your envelopebefore you post it to your friend