The equations of two waves given as $X=acos(\omega t+\delta)$ and $X=acos(\omega t+ \alpha)$, Where $\delta=\alpha+\frac{\pi}{2}$, then resultant wave represent :

Question

( A ) an ellipse (a.c.w)
( B ) a circle (a.c.w)
( C ) a circle (c.w)
( D ) an Ellipse (c.w)