Fix a point $$A$$ from which we draw a clockwise chord. In order for the clockwise chord from another point $$B$$ to intersect that of point $$A$$, $$A$$ and $$B$$ must be no more than $$r$$ units apart.By drawing the circle, we quickly see that $$B$$ can be on $$\dfrac{120}{360}=\dfrac{1}{3}(\rm D)$$ of the perimeter of the crcle. (lmagine a regular hexagon inscribed in the circle). 
在半径为$r$的圆周上独立随机地选择两点．从每一个点沿顺时针方向画出一条长为$r$的弦．这两条弦相交的概率是多少？

a: $$\dfrac{1}{6}$$ 
b: $$\dfrac{1}{5}$$ 
c: $$\dfrac{1}{4}$$ 
d: $$\dfrac{1}{3}$$ 
e: $$\dfrac{1}{2}$$ 