单选题 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