A client with bicuspid aortic valve has severe stenosis and is scheduled for valve replacement. While teaching the client about his condition and upcoming surgery, the nurse shows him a heart illustration. Which valve will be replaced ？（）

A．A

B．B

C．C

D．D

下面对于友元函数描述正确的是（ ）。

A． 多线程就是同时执行几个事件

B． 多线程是将程序分为几个并行的子任务，由它们并发交叉执行

C． 一个进程可产生多线程，形成执行流

D． Java语言支持多线程