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 .
