The magnitude of the magnetic field $$(B)$$ due to loop $$ABCD$$ at the origin $$(O)$$ is

A

zero

B

$$\frac{\mu_0 I (b - a)}{24ab}$$

C

$$\frac{\mu_0 I}{4\pi}\left[\frac{b-a}{ab}\right]$$

D

$$\frac{\mu_0 I}{4\pi}\left[2(b-a) + \frac{\pi}{3}(a+b)\right]$$