1想请教老师一下，for+一段时间是不是可用于任何时态？
如I have not seen him for some time.现在完成时
Andy and Tom talked for three hours.一般过去时
We have been waiting here for some time.现在完成进行时
2怎么区分辨别和使用，现在完成时和现在完成进行时呢？
现在完成时,有表示从过去开始，一直持续到现在的动作，可能还会持续下去
如They have lived in Beijing for five years.
而现在完成进行时有表示一个从过去开始但仍在进行的行动，如：
We have been waiting here for some time.