关于must

题目

关于must
must用来表推测,我做了一趟整理,其中不少是借鉴了百度知道里的,可是出现了一个疑问,请大家指教.
must表推测时：
1.对现在事实的推测,反义部分与must后的动词呼应.例：
You must be joking,aren’t you?
2.对过去事实的推测：表动作时,用did；表状态时,用was.例：
Mr Green must have been punished for his being rude at the meeing,didn’t he?
She must have been a policewoman,wasn’t she?
3.对已发生的过去的情况的推测,若陈述句谓语部分有must have done,且有表示过去的时间状语,问句部分用didn’t；若无表示过去的状况,则用hasn’t或haven’t.
They must have gone there last night,didn’t they?
They must have arrived by now,haven’t they?
They must have been to the Great Wall,haven’t they?
疑点：例句中的She must have been a policewoman,wasn’t she?和They must have been to the Great Wall,haven’t they?
2.对过去事实的推测：表动作时，用did；表状态时，用was。
所以She must have been a policewoman,wasn’t she?应该不是错句子把

答案

must + 完成式.表示对过去的猜测,这条是原则
但是反义部分的时态是根据具体情况来断定的
She must have been a policewoman,是表示对过去的猜测
那反义部分就用wasn’t she
They must have been to the Great Wall
这里的have been to ,是词组,去过某地,是完成的,
所以他不是must + 完成式的形式,不表示过去,表完成
所以用haven’t