Rhombus A B C D has side length 2 and \angle B=120^{\circ}. Region R consists of all points inside the rhombus that are closer to vertex B than any of the other three vertices. What is the area of R ?

**Answer Choices**

A. \dfrac{\sqrt{3}}{3}

B. \dfrac{\sqrt{3}}{2}

C. \dfrac{2 \sqrt{3}}{3}

D. 1+\dfrac{\sqrt{3}}{3}

E. 2