From the following subsets of R³ˣ³, select all that are subspaces R³ˣ³. there may be more than one correct answer.
a. The invertible 3x3 matrices
b. The symmetric 3x3 matrices
c. The 3x3 matrices in reduced row echelon form.
d. The 3x3 matrices with trace 0 (the trace of a matrix is the sum diagonal entries).
e. None of the above.