--- Why did you laugh just now?

--- John wanted to tell us      very funny joke, but he forgot      end himself.

A．/; the

B．a; an

C．a; the

D．the; the

8051单片机共有5个中断源，在同一级别里，5个中断源同时发出中断请求时，程序计数器PC的内容变为（）。

A.000BH

B.0003H

C.0013H

D.001BH