单击命令按钮时，下列程序代码的执行结果为______。 Private Function PickMid(xStr As String) As String Dim tempStr As String Dim strLen As Integer tempStr=“” strLen=Len(xStr) i=1 Do While i＜=strLen/2tempStr=tempStr+Mid(xStr，i，1)+Hid(xStr，strLen-i+1，1)i=i + 1 Loop PickMid=tempStr End Function Private Sub Command1_Click()Dim FirstStr As StringFirstStr=“abcdef”Print PickMid(FirstStr) End Sub

A．abcdef

B．afbecd

C．fedcba

D．defabc