The principal clause should use future tense; while the subordinate clause should use simple present tense. (主句用将来时，从句则用一般现在时)例如：I'll go by bus if it rains tomorrow. If it rains tomorrow, I'll go by bus.
以when，after，as soon as等引导的时间状语从句以及以if，unless等引导的条件状语从句中，如果主句是一般将来时，从句则用一般现在时。I'll tell her the good news when she comes back.如果是祈使句，那么从句通常要用一般现在时。Don’t laugh at me when I make a mistake. 主句是含有情态动词的一般现在时，根据需要从句多用一般现在时。You should be quiet when you are in the reading room.只要表示将来的，都可以
Agent数码Reaper
