must have done不是解释本该做的没做么 怎么有时是对过去的猜测?

问题描述:

must have done不是解释本该做的没做么 怎么有时是对过去的猜测?
有点乱 谁能帮理下~

He must be an asskisser .他肯定是马屁精.(此处指肯定的推测)
He must have finished the task .他肯定完成了任务.(此处是对过去的推测)
对于“本该做什么而没做”要用 should have done .