Before I talked with ______ scientist, I had never met______ clever person like him.

A．the; a

B．a; a

C．the; the

D．a; the

将等产量曲线图和等成本线合在同一坐标平面内，则一条等成本线能且只能与其中一条等产量曲线相切，谅切点就是厂商在成本一定时产量最大(或者产量一定时成本最小)的最佳要素投入组合，即满足厂商均衡条件的点。 ( )