表示从过去某时开始一直持续到现在的动作，并且还将持续下去。
表示在说话时刻之前刚刚结束的动作。
表示一个从过去开始延续到现在，可以包括现在在内的一个阶段内，重复发生的行动。
扩展资料
We are going to have to stop doing that because we cannot find an individual electron.
我们正要停止那么做，因为无法发现一个独立电子。
It may seem inefficient to have two programmers doing“ one programmers job”, but the reverse is true.
让两个程序员去做一个程序员的.工作看起来有些效率低下，但是实际上刚好相反。
We hope to have the pleasure of doing business with you.
我们希望能有与你做生意的乐趣。
I prefer to have a picture when doing this although it is not essential.
我喜欢有一幅当这样做，虽然它并不是必不可少的。
Species from squids to chimpanzees have been caught doing it from time to time.
各物种从鱿鱼到黑猩猩不时被抓到在欺骗撒谎。
