1. have to do
2. have had to do
3. will have to do
4. would have to do
5. would have had to do
5 可以表示:
一、与过去情况不符的虚拟语气:
If the wound had been any deeper, you would have had to go to hospital.
如果伤口再深些,你就得上医院了。
二、对过去所发生情况的推测(肯定程度仅次于must have done):
So she would have had to call him for something.
那她肯定会因什么事情打过电话给他的。