设 $\stackrel{\rightharpoonup }{a},\stackrel{\rightharpoonup }{b}$都是非零向量，下列四个条件中，使 $\frac{\stackrel{\rightharpoonup }{a}}{\left|\stackrel{\rightharpoonup }{a}\right|}=\frac{\stackrel{\rightharpoonup }{b}}{\left|\stackrel{\rightharpoonup }{b}\right|}$成立的充分条件是（  ）

A．	$\left|\stackrel{\rightharpoonup }{a}\right|=\left|\stackrel{\rightharpoonup }{b}\right|$且 $\stackrel{\rightharpoonup }{a}//\stackrel{\rightharpoonup }{b}$
B．	$\stackrel{\rightharpoonup }{a}=-\stackrel{\rightharpoonup }{b}$
C．	$\stackrel{\rightharpoonup }{a}//\stackrel{\rightharpoonup }{b}$
D．	$\stackrel{\rightharpoonup }{a}=2\stackrel{\rightharpoonup }{b}$