--Must I come at four o'clock? --用No,you don't have to.还是No,

--Must I come at four o'clock? 我必须要在4点的时候过来吗?
—No,you don't have to./ No, you needn't. 不,你不需要这样.（不,你并非一定要在4点的时候过来.）

一般习惯用法是这样,Must提问的时候,如果作肯定回答,用Yes, you must. 作否定回答,可以有两种形式.
也就是 Must I .?
------Yes, you must.
------No, you don't have to.
------No, you needn't.

而No,I don't think you have to.这回答,个人感觉如果问句是 Do you think I have to come at four o'clock? 回答No,I don't think you have to.比较对应,前面问“Do you think.” 后面相应地出现有“I think .的字眼”

所以这题应该是--Must I come at four o'clock? --用No,you don't have to.

第一种 简洁 符合口语习惯

都可以，一样d

--Must I come at four o'clock?

我必须要在4点来吗？

1. No,you don't have to 不，你没必要这么做。

2. No,I don't think you have to 不，我认为你没必要这么做。