If A is a 3 x 6 matrix with a row of zeros, and B is a 6 x 4 matrix, then which of the following do we know for sure? A B must have a row of zeros, and A B must have a column of zeros A B may or may not have a row of zeros, but A B must have a column of zeros A B must have a row of zeros, but AB may or may not have a column of zeros Either we cannot guarantee anything about AB, or the product AB doesn't exist. None of the above