已知向量$\stackrel{\rightharpoonup }{a}=(1,2)$，$\stackrel{\rightharpoonup }{b}=(3,1)$，则$\stackrel{\rightharpoonup }{b}-\stackrel{\rightharpoonup }{a}=$

$(-2,1)$ $(2,-1)$ $(2,0)$ $(4,3)$