i'm sorry ___ you about it before.a.not to tellb.not to have told为什么不选a?

i'm sorry ___ you about it before.a.not to tellb.not to have told为什么不选a?
i'm sorry ___ you about it before.
a.not to tell
b.not to have told
为什么不选a?

i'm sorry ___ you about it before.a.not to tellb.not to have told为什么不选a?
b.not to have told
have done 意思是本来应该做,却没有做
我很抱歉,我本来应该提前告诉你,却没有.
祝好!

后面有一个before,已经是完成的事情了

这里是过去完成时，句子中的before已经表示以前，是过去的时间，然后他要表达的意思是在过去之前就告诉他，所以应该用过去完成时