动词时态的替换（1）

用一般过去时代替完成时

1)　两个动作如按顺序发生，又不强调先后，或用then，and，but 等连词时，多用一般过去时。
　　 When she saw the mouse，she screamed.
　　 My aunt gave me a hat and I lost it.

2 ) 两个动作相继发生，可用一般过去时；如第一个动作需要若干时间完成，用过去完成时。
　　 When I heard the news, I was very excited.

3)　叙述历史事实，可不用过去完成时，而只用一般过去时。
　　 Our teacher told us that Columbus discovered America in 1492.


一般现在时代替将来时
时间状语从句，条件句中，从句用一般现在时代替将来时
When, while, before, after, till, once, as soon as, so long as, by the time, if, in case (that), unless, even if, whether, the moment, the minute, the day, the year, immediately


　　He is going to visit her aunt the day he arrives in Beijing. 他一到北京，就去看他姨妈。

典型例题
(1）He said he________me a present unless I_______ in doing the experiment.
　　A. had not given; had not succeeded　　B. would not give; succeed
　　C. will not give; succeed　　　　　　 D. would not give; will succeed.
　 答案B. 在时间，条件或让步主语从句中一般不用将来时。本题有He said，故为过去式。主句用将来时，故选B. 此处用一般过去式代替了过去将来时。

(2) 表示现在已安排好的未来事项，行程等活动。
　 The museum opens at ten tomorrow.　博物馆明天10点开门。(实际上每天如此。)



一般现在时代替过去时
1 )"书上说"，"报纸上说"等。
　 The newspaper says that it's going to be cold tomorrow.
　 报纸上说明天会很冷的。
2) 叙述往事，使其生动。
　 Napoleon's army now advances and the great battle begins.