8.5 cease doing/to do
cease to do 长时间，甚至永远停做某事，cease doing 短时停止做某事，以后还会接着做。例如：
That department has ceased to exist forever. 那个系已不复存在。
The girls ceased chatting for a moment when their teacher passed by. 姑娘们在老师走过时，停了会聊天。
