A thin semi-circular metal ring of radius $$R$$ has a positive charge $$q$$ distributed uniformly over its curved length. The resultant electric field E at the center O is

A

$$-\frac{q}{2\pi^2\epsilon_0 R^2}\hat{j}$$

B

$$\frac{q}{2\pi^2\epsilon_0 R^2}\hat{j}$$

C

$$\frac{q}{4\pi^2\epsilon_0 R^2}\hat{j}$$

D

$$-\frac{q}{4\pi^2\epsilon_0 R^2}\hat{j}$$