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。)