You mustn't tellyour mother,_________ you?

You mustn't tellyour mother,_________ you?
You mustn't tellyour mother,_________ you?

You mustn't tellyour mother,_________ you?
must

must
若陈述部分有mustn’t表示禁止，疑问部分要must：
You mustn’t laugh, must you? 你不准笑，知道吗?