单项选择题
                                            
下列程序代码段中,在单击命令按钮调用SelMid函数时,其运行结果为(    )。    Private Function SelMid(aSlr AS String)As String    Dim temp As String,sLen As Integer    temp="":sLen=Len(aStr)    i=1    Do While i<=sLcn/2    temp=temp+Mid(aStr,i,1)+Mid(aStr,sLen-i+1,1)    i=i+1    Loop    SeMid=temp    End Function    Private Sub Command1_Click()    Dim SirAs String    Str="abcdef":Print SelMid(Str)    End Sub
                                        
                                        
                                            A.abcdef
B.afbecd
C.fedcba
D.defabc