比较法——通过对过去、现在两种不同的倾向、观点的比较，引出文章要讨论的观点。

　　[1] For years, ...had been viewed as .... But people are taking a fresh look now. With the growing ..., people ....

　　[2] People used to think that ... (In the past, ....), But people now share this new idea.