(5)用于在if, unless , even if 引导的条件状语从句中,由When , before , until , as soon as , the moment , once 引导的时间状语从句中,由no matter what/who/which/when /where/how 或 whatever ,whoever, whichever,whenever, wherever, however 引导的让步状语从句中, 这是主句往往用将来时, 或者是祈使句。 I will go as soon as I finish my work . If city noises are not kept from increasing , people will have to shout to be heard even at the dinner table 20 years from now . If you arrive tomorrow , call me . (6)表示按计划,时间表,时刻表规定要发生的动作,限于以下词:begin come , leave , go , arrive , start , stop, return , open , close 等。 The flight takes off at 2:30 every Wednesday and Friday . 2. 现在进行时(am/is/ are + doing ) (1)表示说话时正在进行的动作。 He is doing his homework, while His brother is sleeping now . (2)表示现阶段但不一定是发生在讲话时的一个动作。 Teenagers are damaging their health because they play computer games too much .