How can I get the active tab in a Powerpoint application?

Please I have some questions about:

1/ How can I get the active tab in a Powerpoint application? for example : TabHome is activate or TabInsert

2/ How can I know if the PowerPoint backstage is open? I used the onHide and onShow events but both are running only once.

<backstage onHide="backstageOnHide" onShow="backstageOnShow"> ... </backstage>

I’m using C# and ribbon xml for a VSTO-PowerPoint project.

Thanks a lot.