_____, 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

进度计划里，程控交换系统可以用哪种英文缩写来表示？（）

A.PA

B.PD

C.MPES

D.PABX