From the following subsets of R³ˣ³ select all that are subspaces R³ˣ³ may be more than one correct answer.
A. The invertible 3×3 matrices.
B. The symmetric 3×3 matrices.
C. The 3×3 matrices in reduced row-echelon form.
D. The 3×3 matrices with trace 0 (the trace of a matrix is the sum diagonal entries).
E. None of the above.