— is your brother? —He is ten.[ ]
A. How old
B. Where
C. How
答案：A
—May I swim here?
— No, you _______. It is dangerous.
A．won’t
B．needn’t
C．mustn’t
D．don’t have to
按照逻辑结构分类，结构可以分为线性结构和非线性结构，栈属于______。
