If $\mid \overrightarrow{A}\times \overrightarrow{B}\mid=\sqrt{3} \overrightarrow{A}.\overrightarrow{B}$ then the value of $\mid \overrightarrow{A}+ \overrightarrow{B}\mid$ is:

Question

( A ) $(A^{2}+B^{2}+\frac {AB} {\sqrt 3})^{1/2}$
( B ) $(A^{2}+B^{2}+\sqrt {3}AB)^{1/2}$
( C ) $A+B$
( D ) $(A^{2}+B^{2}+AB)^{1/2}$