Which of these represents a valid elementary row operation?
R1→R1+2R2+3R3R_1 \to R_1 + 2R_2 + 3R_3R1→R1+2R2+3R3
R1→R1×R2R_1 \to R_1 \times R_2R1→R1×R2
R1→R1+0R2R_1 \to R_1 + 0R_2R1→R1+0R2
R1→R12R_1 \to R_1^2R1→R12