Combobox rowsource dependent on option buttons

I have two option buttons on a userform, when the user clicks one of them, I need a combobox to display a dropdown selection. If they click the other option button, I need the dropdown selection to disappear and the combobox to be blank. If someone could help me with the code I'd be very grateful. I've tried an 'If' statement and a 'case', but neither has worked so far - the dropdown selection still appears whichever option you select.

If someone could help me I'd be very grateful, thanks.

I'm not sure if this is exactly what you mean, but should be a good starting point.

BSB