Have you checked the Demo Quiz?
I already answer another Topic from you and now I realize my answer may not work completely.
What I would do is:
Use a button to submit the answer
Button -> On Clicked
First Disable the button (we avoid checking more than once)
If (C and E are checked and B is not checked) do { something }
If (B is checked) do {something}
As you said the B is checked I already have an else button.