how to count checked checkbox in a tab control on a form using vb in VS2017

I have a form, called Form2.
In Form2, there is a tab control, called Tabs.
Tabs has three tab sheets: Tab1, Tab2, Tab3.
In Tab2, there are 5 checkboxes, CB1, CB2, CB3, CB4, CB5.
For CB1, CB2, CB4 and CB5, only one of them could be checked. If more than one are checked, show a meassage box.
How to code in VB? Thanks.