A wire of uniform resistance AΩ/m is bent into a circle of radius r and another piece of wire with length 2r is connected between points A and B (AOB) as shown in figure. The equivalent resistance between points A and B is ____Ω .

A

$$2\pi\lambda r$$

B

$$\frac{3\pi\lambda r}{8} $$

C

$$(\pi+1)2r\lambda $$

D

$$\frac{6\pi\lambda r}{3\pi+16} $$