四级考试常用语法精选（1）

　　Ive been writing letters for an hour.

　　Ive been sitting in the garden.

　　2)过去完成进行时: 过去某个时刻以前一直在进行的动作

　　Id been working for some time when he called.

　　We had been waiting for her for two hours by the time she came.

　　3)将来完成进行时: 将来某个时刻以前一直在进行的动作.

　　By next summer, he will have been working here for twenty years.

　　In another months time shell have been studying here for three years.