(2017•山东) 已知\( A\left(\mathrm{3,0}\right),B\left(\mathrm{2,1}\right)\)，则向量\( \overrightarrow{AB}\)的单位向量的坐标是 ( )
A.\( (1,-1)\)
B.\( (-\mathrm{1,1})\) C.\( (-\frac{\sqrt{2}}{2},\frac{\sqrt{2}}{2})\) D.\( (\frac{\sqrt{2}}{2},-\frac{\sqrt{2}}{2})\)
