[单项选择题] 设有如下通用过程：Public Function Fun(xStr As String)As StringDim tStr As String,strL As IntegerstrL=

[单项选择题] 设有如下通用过程：Public Function Fun(xStr As String)As StringDim tStr As String,strL As IntegerstrL=Len(xStr)Do While i<=strL／2tStr=tStr&Mid(xStr,i,1)&Mid(xStr,strL-i+1,1)i=i+1Loop在窗体上画一个名称为Text1的文本框和一个名称为Command1的命令按钮。然后编写如下的事件过程：Private Sub Command1_Click()Dim S1 As StringTextl.Text=UCase(Fun(S1))程序运行后,单击命令按钮,则Textl中显示的是【 】

A．ABCDEF

B．abcdef

C．AFBECD

D．DEFABC