the toy ( must )be bob'S.he is the only little kid
问题描述：
the toy ( must )be bob'S.he is the only little kid
为什么是不可以是 can be
答
the toy ( must )be bob'S.he is the only little kid
用must
表示强烈的肯定语气推测,用must
can be只是可能是
与其不如must强烈
因为后面说了他是小孩子,所以用must