是is 还是isn't.举例解释一下
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当陈述句中含有must时,反意疑问句有多种构成形式: ①表示推测时,反意疑问句的构成形式举例如下: He must be a visitor, isn't he?(对现在情况的推测) You must have seen him at his birthday party yesterday, didn't you?(对过去情况的推测,且句中有过去的时间状语) You must have seen him at his birthday party,haven't you?(强调动作的完成) ②表示"必须"或"必要"时,其反意疑问句的构成举例如下: They must work hard, mustn't they?(必须) They must take medical lessons, needn't they?(必要)纵上,您给出的例句明显是对现在情况的推测,故答案应选"isn't"。 。