—The two old friends were ____ busy ____ with each other that they forgot the time.

—Yes. They hadn’t met for over ten years, so they kept talking the whole night.       

A．too, to talk

B．too, talking

C．so, to talk

D．so, talking;

当量浓度是：一升（）中所含溶质的克当量数。

A.溶质

B.溶液

C.水分

D.液体