true or false system comprising two linear equations two variables has unique solution if an

True or false: A system comprising two linear equations in two variables has a unique solution if and only if the straight lines represented by the equations are nonparallel.
True or false: Suppose the straight lines represented by a system of two linear equations in two variables are parallel to each other. Then the system has infinitely many solutions.
True or false: If A and B are matrices of the same order, then .
True or false: If A and B are matrices such that AB and BA are both defined, then A and B must be square matrices.
True or false: If A is a square matrix with inverse and c is a nonzero real number, then .
True or false: If AX = B is a system of n linear equations in n unknowns and does not exist, then AX = B does not have a unique solution.