1．We stayed at the Park Hotel last weekend, which a friend of ours recommended (推荐) to us.
2．Social activities usually preserve (保护) the aged from the loneliness of old age.
3．Having bought a precious (宝贵的) diamond necklace for his wife, Martin could hardly afford a tie for himself.
4．He showed good judgement in deciding not to invest (投资) in the project.
5．Were we to do nothing until the knife was sharpened (使变锋利)?
6．Exposure (expose) of the body to strong sunlight can be harmful.
7．There is a general awareness (aware) that smoking is harmful.
8．The invention of paper was a great contribution (contribute) to human civilization.
9．In the course of evolution (evolve), some birds have lost the power of flight.
10．Without the assistance (assist) of my friends, my company couldn't have lived through the hard times.
