友情提示 mikee 网友:

你的三个例句，本身没错。但是，语境则是表语从句或宾语从句，这都要受到主句时态的制约，才用过去完成时的，说明从句的动作早于主句发生，这与 before 没有关系。我认为，before doing... 这个介词短语，跟 before ten o'clock yesterday 没有区别，是一个表达“过去时间点位” 的词组。

The only reasonable conclusion was that they had waited hours before deciding they'd have to get rid of her.

--摘自小说The Marshal at the Villa Torrini

When the deputy asked why he had waited hours before calling police, the 19-year-old said he had been trying to figure out the identity of the thief.

--摘自 英语网站 pjstar

In his interview, Dr. Wang said that he had misdiagnosed his symptoms as those of flu, and that he had waited days before checking himself into a hospital.

--摘自 英语网站 纽约时报

针对此题，我谈谈个人的看法：

He _______ the display for several minutes before re-entering his shop.

a. was gazing at   b. gazed at   c.had gazed at   d.had been gazing at

1. 毫无疑问，此题正确答案为： B. gazed at

2. for several minutes 表示一个动作持续了这段时间后结束。所以排除“进行体”，也就是排除 A。简单地说，现在进行时和过去进行时，都不能跟时间段连用。道理就是，跟了时间段，就意味着动作结束了，违背了进行时的基本概念。

3. “过去完成时” 的参照物，应该有“上文”，本题是个单选题，肯定没有上文。其次，看其他语境，仅仅 before re-entering his shop 是不足以支撑使用“过去完成时” 的。除非改为一个时间从句，加上另外的一个谓语动词，作为“参照物”。前面说过，before doing... 这个介词短语，跟 before ten o'clock yesterday 没有本质区别，是一个表达“过去时间点位” 的词组。

4. 既然过去完成时都不用，那么，过去完成进行时，就更不能使用了。