理论上，分词也是不定式，它们随“主句”的时间变化而变化。但是，它们也的确存在所谓的时间连贯性 ( continuous)问题。

先来个容易理解的：

1. There was an accident that happened yesterday.

2. There was an accident happening yesterday.

句子1很正常，句子2够呛。因为这里出现了所谓的“continuous”问题

对类似的问题，

Hewings在他的Advanced Grammar in Use有写到：

• when the event or action talked about in the defining relative clause comes before the event or action talked about in the rest of the sentence, except when the second event or action is the result of the first. Compare:

• The snow which fell overnight has turned to ice. (not The snow falling overnight...) and
• The snow which fell overnight has caused traffic chaos, (or The snow falling overnight has caused traffic chaos.)

• when we talk about a single, completed action in the defining relative clause, rather than a continuous action. Compare:

• The girl who fell over on the ice broke her arm. (not The girl falling over...) and
• I pulled off the sheets which covered the furniture, (or ...sheets covering the furniture.) 

这些话可作类似问题的参考

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至于，

3. The man preparing documents is my former schoolmate.

4. The man who prepared documents is my former schoolmate.

这个句子，The man preparing documents 这部分并没有体现明显的时间标识，

它应该会有很多的解读，而未必是章教授解读的一种。也就是3的语义，在时间体现上，不仅是4.

非常幸运的是，网上查到一专四题：

65. "The man preparing the documents is the firm's lawyer" has all the following possible meanings EXCEPT
A. the man who has prepared the documents...
B. the man who has been preparing the documents...
C. the man who is preparing the documents...
D. the man who will prepare the documents...

这个答案应该选A，换言之，BCD都是对的