在写作中一定要写完整的句子，即每个句子必须有它的动词(be动词或者实义动词)。一个完整的句子的结构应
该是：1主语 谓语 宾语；2主语 谓语 状语；3主语 谓语 宾语 宾语补足语等句子形式。
1) Small portable machines which generate negative irons. (错)
They have invented small portable machines which generate negative irons. (正确)
2) They enjoy reading classic Chinese Literature. Such as the poetry by Li Bai and Du Fu. (错)
They enjoy reading classic Chinese Literature. such as the poetry by Li Bai and Du Fu. (正确)
注：hence后面可以直接跟名词而独立成句。

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