I must (can't/isn't)see a doctor 换He 做主语 是不是都不用第三人称单数 为什么?那I do not like doctors为什么He doesn't like doctors

问题描述:

I must (can't/isn't)see a doctor 换He 做主语 是不是都不用第三人称单数 为什么?
那I do not like doctors为什么He doesn't like doctors