Present perfect progressive tense 现在完成进行时
1. 现在完成进行时表示从过去某一时刻开始的动作, 一直延续到说话时还在进行或可能还要继续下去。句中常出现for, since, how long等引导的时间状语。例如:
(1) Her telephone has been ringing for a long time.