The meeting has been called off. has后为什么加been. 谢谢

The meeting has been called off. has后为什么加been. 谢谢 The meeting has been off for two hours.It______since_______. 请问：the meeting has been on for over ten mimutes.中为什么加ON? there has been...为什么要加been? C) 19.I heard the sports meeting has been put off until ____ 一道关于时态的英语题--I ____ the sports meeting has been put off.--Yes I don't think that the meeting has been put off,_________? The meeting has been put off by an hour.是被动语态? You _____.The school sports meeting has been put off.A.needn The ice has been melted .为什么这个现在完成时要加been,been不是被动语态吗? A new machine called 'The Revealer' has been invented mark twain has been called the inventor...中文翻译