A wire of resistor R is bent into a circular ring of radius r. Equivalent resistance between two points X and Y on its circumference, when angle XOY is a, can be given by

• A.            \[\frac{R\alpha }{4{{\pi }^{2}}}(2\pi -\alpha )\]
• B.            \[\frac{R}{2\pi }(2\pi -\alpha )\]
• C.            R (2p ? a)
• D.            \[\frac{4\pi }{R\alpha }(2\pi -\alpha )\]