As a general rule, it goes as follows:
Switch:- Off Left Right Both
Off = Both mags grounded (won't supply ignition)
Left = Left magneto live and right magneto grounded (Left will supply ignition)
Right = Right Magneto live and left magneto grounded (Right will supply ignition)
Both = Both Mags live and will supply ignition.
Disclaimer: In my experience, a lot of aircraft that are older have had many wiring repairs and even new looms fitted which can lead to the switch doing the opposite to the above chart. However, the switch is supposed to be Off Left on Right on Both on.
I wouldn't be surprised if the correct answers in your exams are as confused as some of the aircraft wiring out there.
To be 100% on this, you'd need to verify it by sifting through some wiring diagrams on various ME trainers to be sure.
Cheers