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【正】Unit 5Ⅰ.重点句式1.It has been proven again and again that frequent advertising in- creases product sales.经常做广告会增加产品的销售,这是一再证明了的。it可以充当形式主语,指代后面的that从句。例如:It is said that we’ll have a test soon.据说我们很快就要考试了。