1.I have been waiting for you at the school gate for 3 hours in such a hot day.
2.I have been studying day and night since I was admitted to this senior high school.
3.How many times has this old professor been to America?
4.How long have you been living alone in this small town?
5.They have mastered many techniques for studying well so far.
6.This is the first time that I have undergone such a serious failure.
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