Gravitational field at the centre of a semicircle formed by a thin wire AB of mass M and length l is

(a) $\frac{GM}{l^2}\mathrm{along} x-\mathrm{axis}$                               (b) $\frac{GM}{\mathrm{\pi }{l}^2}\mathrm{along}\mathit{ }y-\mathrm{axis}$
(c) $\frac{\mathit{2}\pi GM}{l^2}\mathrm{along} x-\mathrm{axis}$                          (d) $\frac{\mathit{2}\mathrm{\pi }GM}{l^2}\mathrm{along} y-\mathrm{axis}$