20. Three equilateral triangles with sides of length 1 are shown shaded in a larger equilateral triangle. The total shaded area is half the area of the larger triangle.
What is the side-length of the larger equilateral triangle?
A $\sqrt{5}$
B $\sqrt{6}$
C $\frac{5}{2}$
D $\frac{3 \sqrt{3}}{2}$
E $1+\sqrt{3}$