20.  Which of the following statements are correct?

(A) A linear system with fewer equations than unknowns may have no solution.

(B) Every linear system with the same number of equations as unknowns has a unique solution.

(C) A linear system with coefficient matrix A has an infinite number of solutions if and only if A can be row-reduced to an echelon matrix that includes some column containing no pivot.

(D) If [A|b) and [B|c] are row-equivalent partitioned matrices, the linear systems Ax = b and Bx = c have the same solution set.

(E) A linear system with a square coefficient matrix A has a unique solution if and only if A is row equivalent to the identity matrix.