Which of the following formulas define norms on $\mathbb{R}^3$ ?
(a) $\|\mathbf{v}\|=\sqrt{2 v_1^2+v_2^2+3 v_3^2}$,
(b) $\|\mathbf{v}\|=\sqrt{v_1^2+2 v_1 v_2+v_2^2+v_3^2}$
(c) $\|\mathbf{v}\|=\max \left\{\left|v_1\right|,\left|v_2\right|,\left|v_3\right|\right\}$,
(d) $\|\mathbf{v}\|=\left|v_1-v_2\right|+\left|v_2-v_3\right|+\left|v_3-v_1\right|$,
(e) $\|\mathbf{v}\|=\left|v_1\right|+\max \left\{\left|v_2\right|,\left|v_3\right|\right\}$.