根据所给单词的适当形式填空。
Our Chinese teacher asked us to write a 400-word __________ (composition)about the autumn. I think it’s easy.
—What has_________(happen) to your hometown recently?
—Great changes have taken place.
We have taken some _________(measure) to look for the lost boy. We can find him in danger.
We have ________(learn) a lot of knowledge from the wonderful trip.
Not all people know that light pollution does great __________ (harmful) to human’s health.