7、我认为这不值得一试。 误：I think this is not worth trying. 正：I don't think this is worth trying. 英语中表臆想、猜测的动词think, believe, fancy, expect, guess, imagine, suppose等，如果带有否定的宾语从句，宾语从句中的否定词通常提前，用来否定主句的谓语动词。尤其是think, 按习惯用法，否定词只能置于think前。
　　8、他来这儿不是为了求得我们的帮助。 误：He came here not to ask us for help. 正：He did not come here to ask us for help. 否定状语时，英语中的否定词一般不直接置于被否定词语前，通常置于谓语动词前。只有当两个部分加以对比时，即"不是……而是"时，否定词才可直接置于状语前。如：他来这儿不是为了求得我们的帮助，而是来给我们提供一些信息。He came here not to ask us for help, but to give us some information.即使在这一结构中，英语还是常把否定词置于谓语动词前。
　　9、他的设计肯定还没完成。 误：He mustn't have completed his design. 正：He can't have completed his design. 对比较有把握的推测，肯定句中用must，而否定句中用can't，对过去的推测，在must和can't后接完成形式。