123. The student carefully        to the headmaster that his late arrival was caused by traffic jam.

A．told

B．explained

C．exposed

D．Talked

矿井在正常生产情况下，平均每生产1吨煤所涌出的瓦斯量称为（）。

A.总计瓦斯涌出量

B.绝对瓦斯涌出量

C.相对瓦斯涌出量

D.单位瓦斯涌出量