英语动词时态问题1． There (be) - have been-- several such occurrences

英语动词时态问题1． There (be) _ have been__ several such occurrences in the past few weeks.在过去的几个星期,发生了几宗事故.为什么不用had been ,不是说在过去的几个星期吗?2． We are going to Florida as soon as we (finish) _finish_____ taking our final exams.为什么用 finish 是因为 be going to do 3． A lot of people were standing around when the police (arrive) _arrived___________.根据主句’ were standing around’,状语从句不应该用 was arriving 1、3都可以理解了,2还是不太明白,是否理解为因为'be going to'表将来,所以从句用一般现在时来表将来时？