关于反意疑问句的问题You must finish it ,mustn't you You must have fini

反意疑问句中含有Must的情况主要两种：
一、must作为情态动词表“必须”,这时反意疑问句直接用mustn'/needn't
二、must表推测,译作：“一定是...”.当must表示推测时又分以下几种情况：
1、对现在事实的推测,反意疑问句与must后面的动词呼应,如:
1)、You must be joking,aren't you
2)、He must be there,isn't he?
3)、He must have a big family,doesn't he?
4)、He must be waiting outside,isn't he?
5)、There must be some students in the room,aren't there?
2、对已发生的过去情况的推测,若陈述句谓语部分有“must have done”,而且有表示过去的时间状语,问句部分用didn't；若没有表示过去的时间状语,问句部分用haven't或hasn't.如：
1)They must have gone there last night,didn't they?
2)They must have arrived by now,haven't they?（根据by now来判断）
3)They must have been to the Great Wall,haven't they?
若是被动句,应按被动结构来处理.如：
1)The room must have been cleaned yesterday,wasn't it?
2)The room must have been cleaned,hasn't it?

You must finish it ,mustn't you ?你一定要把它完成，不是吗？可以理解成：你一定要把它完成，难道不一定吗？
You must have finished it ,haven't you ?你一定已经完成它了，不是吗？可以理解成：你一定已经完成它了，难道你没有完成吗？

这是个事态问题，第一句用的是一般现在时，第二句用的是现在完成时。

第一句用的是带有情态动词的一般现在时，第二句用的是带有情态动词的现在完成时。