1. 表示因果类关键词：

　　as a result, result in, result from, lead to, because of, due to, contribute to, owning to, hence, since, accordingly, consequently, therefore, in that, etc.

　　2. 表示转折类关键词：

　　despite, in spite of, but, although, though, while, yet, otherwise, on the other hand, however, nevertheless, nonetheless, etc.

　　3. 表示比较类关键词：

　　more, than, less, the least, the most, prefer, equally, likewise, similarly, in comparison, as…as, etc.