在窗口中多个复选框控件，分成两组，如何设置两组内的复选框不能同时选择？

Dim a1 As WinForm.CheckBox = e.Form.Controls("CheckBox1")
Dim a2 As WinForm.CheckBox = e.Form.Controls("CheckBox2")
Dim a3 As WinForm.CheckBox = e.Form.Controls("CheckBox3")
Dim a4 As WinForm.CheckBox = e.Form.Controls("CheckBox4")
Dim a5 As WinForm.CheckBox = e.Form.Controls("CheckBox5")
Dim a6 As WinForm.CheckBox = e.Form.Controls("CheckBox6")
Dim a7 As WinForm.CheckBox = e.Form.Controls("CheckBox7")
Dim a8 As WinForm.CheckBox = e.Form.Controls("CheckBox8")
If a1.Checked = True Or a2.Checked = True Or a3.Checked = True Or a4.Checked = True Then
a5.Checked = False
a6.Checked = False
a7.Checked = False
a8.Checked = False
End If
If a5.Checked = True Or a6.Checked = True Or a7.Checked = True Or a8.Checked = True Then
a1.Checked = False
a2.Checked = False
a3.Checked = False
a4.Checked = False
End If

这样设置后5，6，7，8不能选择了，老师帮我看看阿有其他办法？谢谢老师