this was the third time they()china.为什么括号中填had visited,this+be+the first

是的.不为什么,记住就是.学语言最忌讳追根溯源了.结果语言没学会,考古没成功 ：）
当然要是已经做过的事,如果没做还得用别的时态,如：
This is the first time I shall visit the city.
=This is the first time for me to visit the city.
如果已经做了,不可用一般过去时,而应该是完成式,前面是is的话,用现在完成时,是was便用过去完成时
如：This is the 2nd time I have seen the film.
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