和国内学生写文章不一样,美国人的阅读文章中从来都不出现“I think that,in my opinion,as far as I am considered”此类语言做主题句。通常来说主题句有以下两种形式:
1. 判断句(含情态动词,系动词,正负褒贬词的句子);
2. 概括文章将来结构。
比如一个句子:Your minds changed my attitude. 这句话中并没有情态动词和系动词,因此这句话自然不是判断句,也就不是主题句。但只要在这句话中加入一个正负褒贬词,即一个词表明作者的态度或观点的词即是判断句了。比如,Your minds successfully changed my attitude即是判断句了。
另外,如果一个句子不是判断句,只要它能够概括文章将来结构,及文章后面会从哪几个方面来说明,也是主题句。比如,People are living longer now. 这句话一定不是主题句,而如果这句话是,People are living longer now since the improvement of food condition and the development of medical technology.这句话即是主题句了。因为它概括了文章后面会从哪几个方向来进行说明。
比如一篇文章的开头是,Mycorrhizal fungi infect more plants than do any other fungi and are necessary for many plants to thrive, but they have escaped widespread investigation until recently for two reasons. First, the symbiotic association is so well-balanced that the roots of host plants show no damage even when densely infected. Second, the fungi cannot as yet be cultivated in the absence of a living root.