Since no one has answered this yet, perhaps I need to make it more clear what I was thinking.
I thought that if I can conclude that dim(N(A)) = 0, then the rank = 3. As in an M x N matrix, N = Rank + Nullity. Therefore, since the rank is 3 and n = 3, a basis for the column space would have to be the 3 columns.
Am I correct in thinking this?