Two is enough.为什么用is?主语是?

Two is enough ,为什么谓语动词用的是单数呢?而 Ten of them are teachers 却是复数 two more days is enough Two hours is enough for us to finish the experiment为什么要用介词fo Two thousand dollars is enough for the car.此句里的be动词为什么用is而不是 Two glasses---------enough填is 还是 are 5 dollars is enough 为什么用is dollars 是复数啊 Two day is enough.3kilometers is not far from. Taking photos is interesting 主语是Taking photos 如果是那为什么要用is 不用 is there a library near here?yes .there is .为什么there是主语吗?可以用 enough is not enough enough is Another two days （ is/are ） enough.选哪个?