I do agree with whitebearbother! actually what he said is really right! Take it what I advise here,because I am a teacher of English, who have been solve the same question.
祈使句的疑问附加句用will you 和 won't you 均可。 在这里以用 won't you 为好。此句话并不是提出疑问，而是向对方提出请求，肯定的意念，既“你和杯茶吧”。故答案应选 C
中学的语法里，这个叫做祈使句的反意疑问句。用will you/won't you. 在这里，应该用won't you. C 而若前面是Don't have a cup of tea,则用will you.
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