山区河流的砂主要来自什么时候？
参考答案：
主要来自汛期暴雨的冲刷。
A ruler and a pen ________ in the Lost and Found. [ ]
A. is
B. are
C. has
D. have
----I think the teacher is wrong, _____?
----No, I don't think so
A．don't you
B．don't I
C．doesn't he
D．doesn't she
