14是虚拟语气题,前面说的是过去的事实,后面是去过去的事实相反的所以用A,并且用了明显的连词otherwise,否则例子给你一个you helped me a lot,otherwise i could have not succeeded.
16同样是虚拟啊,是情态动词加have done 结构,need not have done 没必要做却做了,done 省略了 前面重复的动作,语义明确,可以省,给你情态have done几个归纳,should have done本应该做却没做,shoud not have done 本不应该做却做了,could have done本可以做却没做,你们应该学过了吧
19是强调句型啊,强调的是主语,这个一说你应该就知道的,还有强调句,常考not until 强调
给你个例子,we did not read until the teacher came in
it is not until the teacher came in that we read .就是 not until要放被强调部分