1.The book must be lucy's,isn't it?
2个回答

1The book must be lucy's,isn't it?这句里面有Be,所以后面用isn't it?

The girl mustn't go out,must she?这句没有be ,只有情态动词must,并且前面是否定,所以后面直接用must she?要是前面是肯定,后面就用否定疑问.

2 这里是把主语强调成集体,后面就用单数了.强调 个数,成员的话 就用复数