_____, he talks a lot about his favorite singers after class.

A．A quiet student as he may be

B．Quiet student as he may be

C．Be a quiet student as he may

D．Quiet as he may be a student

下列事故统计指标中，属于相对指标的是（）。

A.千人死亡率 

B.伤害严重率 

C.重伤人数 

D.直接经济损失