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■若其中的动词be为现在式（am, is, are），则其后不定式通常只能是静态动词，不能是动态动词。如：They are fortunate to be able to buy such a large a house. 他们真幸运，能买那样大的房子。但不能说：They are fortunate to buy such a large house.■若要在am [is, are] fortunate后接动态动词，则要用完成式或进行式。如：They are fortunate to have bought such a large house.他们很幸运，买了那样大的房子。You are fortunate to be working in London. 你真是幸运，能在伦敦工作。■若其中的动词be为过去式（was, were），则其后不定式便没有以上限制。如：He was extremely fortunate to escape without injury. 他能安然无恙地逃脱，真是太幸运了。He was fortunate to have had the chance of doing so. 他很幸运有机会这样做。■be fortunate后接不定式与接从句意思稍有不同：It is fortunate that…的意思是“……是件好事”，而“主语+be+fortunate to do sth”则强调主语的好运气。如：It’s fortunate for us that he has a rich uncle 他有一位有钱的叔叔是我们的运气。（如可以替我们借钱）He’s fortunate to have a rich uncle. 他真幸运有一位有钱的叔叔。（许多人没有）