Music Theory - Scales

I have a test in music theory in an hour and a half and need tips to distinguish the difference while listening to natural, harmonic, and melodic minor scales and ionian, lydian, and mixolydian major scales. I think all the minor scales have a flat on the third note, and I can do those alright, but I'm having a hard time with the major scales. Any tips?

Edit: Also, how do you tell the difference between a minor 6th, major 6th, minor 7th, and major 7th intervals? Probably hard to describe but they all sound the same to me.