四、含有非谓语动词的句子
　　非谓语动词包括：动词不定式、动名词、现在分词和过去分语。使用非谓语动词可以用较少的词表达同等甚至更加丰富的信息，使句子结构紧凑、逻辑严谨。

　　如：
　　原句：It must be realized that people should be cautious when they decide which books they should choose to read since if they read bad books , it will be time-wasting and harmful .
　　优化：It must be realized that people should be cautious when deciding which books to read since reading bad books in time-wasting and harmful .
　　原句：Because one of my parents is laid off , my family can't possibly afford all my expenses at college .
　　优化：With one of my parents being laid off , my family can't possibly afford all my expenses at college .