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(aStr As String)As String Dim temp As String Dim sLen As Integer temp= sLen=Len(aStr) i=1 Do While i＜=sLen 2 temp=temp+Mid(aStr,i,1)+Mid(aStr,sLen-i+1,1) i=i+1 Loop SelMid=temp End Function Private Sub Command1_Click() Dim Str As String Str= abcdef :Print SelMid(Str) End Sub
A．abcdef
B．afbecd
C．fedcba
D．defabe