Sometimes a good test of common sense though. We got a question in our Systems exam about something that no one in the class could remember seeing in our notes / mentioned by the instructor which caused a mass scratching of heads in the exam room.
Like everyone else I didn't know the answer, but remarkably, I was the only one to spot that it was sandwhiched between questions on ignition systems, and only answer "(c) Magneto" had anything to do with ignition systems!
BTW I thought Gen Nav was easy too! One third CRaP 5 questions; easy. One third instruments questions; small bank of feedback covered every single one. Final third proper questions; listened to what my instructor said came up regularly and I had an easy peasy pass.