Three circles of radius 1 are externally tangent to each other and internally tangent to a larger circle. What is the radius of the large circle?
Answer Choices
A. \dfrac{2+\sqrt{6}}{3}
B. 2
C. \dfrac{2+3 \sqrt{2}}{3}
D. \dfrac{3+2 \sqrt{3}}{3}
E. \dfrac{3+\sqrt{3}}{2}