Which of the following subsets of R^(3x3) are subspaces of R^(3x3)?

A. The invertible 3 x 3 matrices

B. The 3 x 3 matrices with determinant 0

C. The symmetric 3 x 3 matrices

D. The diagonal 3 x 3 matrices

E. The 3 x 3 matrices in reduced row-echelon form

F. The 3 x 3 matrices with trace 0 (the trace of a matrix is the sum of its diagonal entries)

I am not even sure how to begin, do you still apply the closure properties, if so how? Thank you for any help!