若向量 $\stackrel{\rightharpoonup }{a}=\left(2,0\right),\stackrel{\rightharpoonup }{b}=\left(1,1\right)$，则谢列结论正确的是（）

A．

$\stackrel{\rightharpoonup }{a}·\stackrel{\rightharpoonup }{b}=1$

B．

$\left|\stackrel{\rightharpoonup }{a}\right|=\left|\stackrel{\rightharpoonup }{b}\right|$．

C．

$\left(\stackrel{\rightharpoonup }{a}-\stackrel{\rightharpoonup }{b}\right)\perp \stackrel{\rightharpoonup }{b}$

D．

$\stackrel{\rightharpoonup }{a}\parallel \stackrel{\rightharpoonup }{b}$