Matrix B only
A matrix is in row echelon form if
- all nonzero rows (rows with at least one nonzero element) are above any rows of all zeroes (all zero rows, if any, belong at the bottom of the matrix), and
- the leading coefficient (the first nonzero number from the left, also called the pivot) of a nonzero row is always strictly to the right of the leading coefficient of the row above it (some texts add the condition that the leading coefficient must be 1
Source: Wikipedia https://en.wikipedia.org/wiki/Row_echelon_form
