For any two vectors $\vec{a}$ and $\vec{b}$, which of the following statements is always true ? (A) $\vec{a} \cdot \vec{b} \le |\vec{a}| |\vec{b}|$ (B) $|\vec{a} + \vec{b}| \ge |\vec{a}| + |\vec{b}|$ (C) $|\vec{a} - \vec{b}| = |\vec{a}| - |\vec{b}|$ (D) $|\vec{a} \times \vec{b}| \ge |\vec{a}| |\vec{b}|$