关于向量下列说法错误的是（   ）

A：如果 $\stackrel{\rightharpoonup }{a}=\lambda \stackrel{\rightharpoonup }{b}$ ，则 $\stackrel{\rightharpoonup }{a}//\stackrel{\rightharpoonup }{b}$

B：如果 $\stackrel{\rightharpoonup }{a}\cdot \stackrel{\rightharpoonup }{b}=0$ ，则 $\stackrel{\rightharpoonup }{a}\perp \stackrel{\rightharpoonup }{b}$

C：$\left|\stackrel{\rightharpoonup }{a}\cdot \stackrel{\rightharpoonup }{b}\right|\le \left|\stackrel{\rightharpoonup }{a}\right|\left|\stackrel{\rightharpoonup }{b}\right|$ ，当且仅当 $\stackrel{\rightharpoonup }{a}$ 与 $\stackrel{\rightharpoonup }{b}$ 共线时取等

D：$\left|\stackrel{\rightharpoonup }{a}+\stackrel{\rightharpoonup }{b}\right|\le \left|\stackrel{\rightharpoonup }{a}\right|+\left|\stackrel{\rightharpoonup }{b}\right|$ ，当且仅当 $\stackrel{\rightharpoonup }{a}$ 与 $\stackrel{\rightharpoonup }{b}$ 共线时取等