Watch the Example 7 online guitar lesson by Brad Carlton from Guitar Lab: Boogie-Woogie

This passage modifies ex 6 by changing the 2nd voice in the third chord from C# to C. This is an example of mixed mode harmony. The 1st chord is A, 2nd chord is Bm/A. The 3rd chord is C/A (Am7) and the 4th chord is Bm/a. The A chord comes from A mixolydian, the Bm/A could come from A dorian or A mixolydian and the C/A (Am7) comes from A dorian. This passage straddles the fence between A Major and A minor tonality (or A dominant and A minor tonality).