单击窗体时,下列程序的执行结果是 Private Sub Invert(ByVal xstr As String, ystr As String) Dim tempstr As String Dim I As Integer I=Len(xstr) Do While I >=1 tempstr=tempstr + Mid(xstr, I, 1) I=I - 1 Loop ystr=tempstr End Sub Private Sub Form_Click() Dim s1 As String, s2 As String s1= 'abcdef' Invert s1, s2 Print s2 End Sub( )。