I've notice the C minor excercises belongs to Eb major scale, a major 6 interval. The flat E A B which is the 3rd 6 and 7th notes of the C major scale is now the 1st 4th and 5th note of Eb major scale. I think this is to accommodate the major scale intervals. What I have here is a guide to all the Keys and their signatures and I notice the flat notes of Eb major scale matches the flat notes of the C minor scale.