它们一般都用与主将从现：
If / as soon as she comes tomorrow,she will tell us about her last week's trip in Japan.
这里的as soon as 和if 都是连接词,即便它们指代的事物是将来发生的,come这个动词不能用will come,只能用一般现在时.它的主句是一般将来时或祈使句,如
Come if / as soon as you are free next week.==As soon as / if you are free next week,come.
也有---主过从过----但它必须用于过去时间i( if 这个结构不包括在内）.如,
As soon as I got the news yesterday,I told Tom==== I told Tom the news yesterday as soon as I got it.请比较以下句子
1 He says that he will come tomorrow if / as soon as he is free.
2 He said that he would come the next day if / as soon as he was free.
