你说的没错，那个是general grammar rule吧。

http://faculty.washington.edu/marynell/grammar/reprtdsp.html

这里说

*Exceptions:

• If the reported sentence deals with a fact or general truth, the present tense is (can be) retained. She said that the moon causes the tides.

• If the speaker reports something immediately or soon after it was said, the noun clause verb often remains as spoken.
  A: What did the conductor say?
  B: He said that the next stop is Northgate.
• If will is the modal in the reported utterance and expresses future time, and if the situation described in the quote still holds true at the time of the indirect report, the will may not be changed to would even though the reporting verb is in the past tense:
  Mr. Arden said that a volcanic eruption will occur next year.

所有跟帖： 

• Good one. Thanks. -EnLearner- ♀ (0 bytes) () 09/02/2011 postreply 21:08:54

• The date change rules are also kind of new to me. -jennea- ♀ (2490 bytes) () 09/02/2011 postreply 21:16:38

• Thank you, Ms. Google. :-) -EnLearner- ♀ (0 bytes) () 09/02/2011 postreply 21:20:06

• 谢谢jennea恩仙！现在我明白了！ -beautifulwind- ♀ (0 bytes) () 09/02/2011 postreply 21:22:04