In other words, all of the above.
============================================
Explanation:
Since matrix A, B, and C are all the same size (3 by 3), this means we can add them. Addition is defined. Multiplication is also defined in this case.
A few of the many properties of matrix addition and multiplication are
Keep in mind that the last property is not the same as (B+C)*A because the order of multiplication matters. A*B is not the same as B*A.
Based on those points above, we can see that all statements your teacher mentioned are true ones.