Here's what I would have submitted:

Question 1:
    [-5]        [-5]        [ 1] 
    [ 1]        [ 0]        [ 0]
x2 *[ 0] + x4 * [-2] + x6 * [ 2]
    [ 0]        [ 1]        [ 0]
    [ 0]        [ 0]        [-1]
    [ 0]        [ 0]        [ 1] 

Question 2:

A, B, D, and M.  They have pivots in every row.

Question 3:
B.  It's the only one with a pivot in every column.