托福写作不仅仅要凑够字数，想要拿到高分可是有很大讲究的哦，留学群托福栏目为大家整理托福写作中如何正确使用逗号，希望对大家有所帮助!
1.在并列连词(and， but， for， nor， or， yet )前使用，用来连接托福写作中的各分句。
The principal reason for this is that none of them possesses chlorophyll，and since they cannot synthesize their own carbohydrates， they obtain their supplies either from the break down of dead organic matter or from other living organisms.
2.用逗号来分隔一系列单词、词组和从句。
Further more the walls of fungal cells are not made of cellulose， as those of plants are， but of another complex sugar like polymer called chitin， thematerial from which the hard outer skeletons of shrimps， spiders， and insects are made.
They are a major cause of structural damage to building timbers， a cause of disease in animals and humans， and one of the greatest causes of agricultural losses.
3.逗号用来分隔与句子其他部分密切相连的简短插入语或旁白。(较长的，更为突兀的或复杂的插入成分的则用破折号或圆括号。)
Chemical fertilization，for example， helps to produce better crops， but is harmful to the environment.
4.在并列形容词，即分别修饰同一个名词的形容词之间使用逗号，但也有的形容词之间不加逗号的。
For men， heroism was usually described as bravery and the active，successful over coming of adversity.
5.在新托福写作中，用逗号来分隔非限定性修饰语，即该修饰语对于句子的意义并非必不可少。非限定性修饰语与限定性修饰语的区别在于，它即使被省略，也不会改变句子的主要意思。
(1) 同位语。
The canopy， the upper level of the trees in the rain forest， holds aplethora of climbing mammals of moderately large size， which may includemonkeys， cats， civets， and porcupines.
(2) 从句。
The canopy， the upper level of the trees in the rain forest， holds aplethora of climbing mammals of moderately large size， which may includemonkeys， cats， civets， and porcupines.
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