根据所给单词的适当形式填空。
【小题1】Our Chinese teacher asked us to write a 400-word position （position）about the autumn. I think it’s easy.
【小题2】—What hashappened (happen) to your hometown recently?
—Great changes have taken place.
【小题3】We have taken some measures (measure) to look for the lost boy. We can find him in danger.
【小题4】We have learnt/learned (learn) a lot of knowledge from the wonderful trip.
【小题5】Not all people know that light pollution does great harm (harmful) to human’s health.
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解析：此题重点考查单词形式的正确运用。