In a uniform linear array, four isotropic radiating elements are spaced $$\frac{\lambda}{4}$$ apart. The progressive phase shift between the elements required for forming -
the main beam at $$60^\circ $$ of the end fireis:

A

-$$\pi$$

B

-$$\frac{\pi}{2}$$

C

-$$\frac{\pi}{4}$$

D

-$$\frac{\pi}{8}$$