Go with what you know
I found the OAT Met. cd worked for me. If there is a Gen. Nav. equivalent, go with that, then.
Thrash through your groundschool examples, however, and it will come good; I would suggest that you hit the BGS database, but only do so when you understand the concepts. I found that helps you to eliminate the two nonsense answers immediately and gives a grace period for working out the two likely candidates with reason rather than hope.