矿石类型与矿石品级边界线
参考答案：
据矿石类型和矿石的技术路线来确定的边界线，常指在可采边界内不同矿石类型和技术品级的边界线。
— Look, that’s Tom—the lost boy!
— It’s really_______great comfort to see him safe again. He is sure to bring_______comfort to his worried mother.
A．a; a
B．the; the
C．a; /
D．the; /
在图中画出合适的透镜．
