the owner must be a boy(否定) the owner——be a boy

问题描述:

the owner must be a boy(否定) the owner——be a boy

在这里must是表推测的 拥有着一定是个男孩
因此否定 也是表推测 肯定不是 所以只能用can't
The owner can't be a boy.
希望能够帮到楼主