题目

关于新概念英语一道时态问题（救急!）
关于2册86课中的
1）...They had just had enough time to swim out of danger when the boat again completed a circle. ...中为什么后面一句不加had?即为何不是“when the boat had again completed a circle.”?
2）还有...On this occasion, however, it had slowed down considerably.The petrol had nearly all been used up. Before long,the noise dropped completely and the boat began to drift gently across the water. ... 中最后一点为什么不用完成式?
即为何不是“the noise had dropped completely”?这样明明还通顺一点?
为什么?
（答案满意再多加分）

提问时间：2020-07-26

答案

1.when the boat again completed 在had enough time to swim out of danger 之前,所以用过去完成时.
2.the noise dropped completely and the boat began to drift gently across the water.这一句话中两个动词用and连接,所以时态相同,过去完成时态一般在句子中有两个分句,其中一个与另一个有时间上的先后,一个句子用过去式的基础上使用