几个高二英语完成句子~weshouldconsiderwhatuse___(能利用)suchabookAllflights_____(被取消)becauseofthesnowstorm,manypassengerscoulddonothingbuttakethetrain(cancel)答案是“havingbeencanceled”为什么要用

　　几个高二英语完成句子~

　　weshouldconsiderwhatuse___(能利用)suchabook

　　Allflights_____(被取消)becauseofthesnowstorm,manypassengerscoulddonothingbuttakethetrain(cancel)答案是“havingbeencanceled”为什么要用完成时啊

　　______(排队等了半个小时),theoldmansuddenlyrealizedhrhadleftthechequeinthecar.(wait)答案是“Waitinginthequeueforhalfanhour”为什么不用“Havingbeenwaiting?”