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

没有如图所示窗体和以下程序：

Private Sub Command1_Click( )
Text1. Text = "Visual Basic"
End Sub
Private Sub Text1_LostFocus( )
If Text1. Text ＜＞ "BASIC" Then
Text1. Text = " "
Text1. SetFocus
End If
End Sub
程序运行时，在Text1文本框中输入“Basic”(如图所示)，然后单击Command1按钮，则产生的结果是( )。

A) 文本框中无内容，焦点在文本框中
B) 文本框中为“Basic”，焦点在文本框中
C) 文本框中为“Basic”，焦点在按钮上
D) 文本框中为“Visual Basic”，焦点在按钮上