If a matrix A = $\begin{bmatrix$}[r] 0 & 1 \ 2 & -1 \end{bmatrix} and matrix B = $\begin{bmatrix$}[r] 3 \ 1 \end{bmatrix}, then which of the following is possible :

1. A + B

2. A - B

3. AB

4. BA

If M × $\begin{bmatrix$}[r] 3 & 2 \ -1 & 0 \end{bmatrix} = \begin{bmatrix}[r] 3 & -1 \end{bmatrix}, the order of matrix M is :

1. 2 × 2

2. 2 × 1

3. 1 × 2

4. 1 × 3

If matrix A = $\begin{bmatrix$}[r] x - y & x + y \ y - x & y + x \end{bmatrix} and matrix B = $\begin{bmatrix$}[r] x + y & y - x \ x - y & y + x \end{bmatrix}, then A + B is :

1. $\begin{bmatrix$}[r] 2y & 2x \ 0 & 2(x + y) \end{bmatrix}

2. $\begin{bmatrix$}[r] 2x & 2(x + y) \ 0 & 0 \end{bmatrix}

3. $\begin{bmatrix$}[r] 2x & 2y \ 0 & 2(x + y) \end{bmatrix}

4. $\begin{bmatrix$}[r] 2x - 2y & 2y \ 0 & 0 \end{bmatrix}

Event A : Order of matrix A is 3 × 5.

Event B : Order of matrix B is 5 × 3.

Event C : Order of matrix C is 3 × 3.

Product of which two matrices gives a square matrix.

1. AB and AC

2. AB and BC

3. BA and BC

4. AB and BA