1.我们应该阻止他吸烟.  (stop-----from doing------)
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2.乱扔纸和金属品是浪费行为.(It's +adj. + to do sth.)
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3.环境能对我们的日常活动产生重大影响.(make a difference to)
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4.空气污染对我们的健康有害.(do harm to)
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