一般现在时：I clean the window.一般过去时：I cleaned the window.现在完成时：I have cleaned the window.一般将来时：I will clean the window.现在进行时：I am cleaning the window.过去进行时：I was cleaning the window.现在将来进行时：I will be cleaning the window.现在完成进行时：I have been cleaning the window (for the past 2 hours)后面需跟具体的时间段，或者by+时间点过去完成时：I had cleaned the window (before I had lunch). 需要一个过去时间点作为参照。供参考。