If $\alpha$ is a non-real root of $x^6=1$, then $\large\frac{\alpha ^5+ \alpha ^3+ \alpha +1}{\alpha ^2+1}$ is equal to :

Question

$$\begin {array} {1 1} (a)\;\alpha^2 & \quad (b)\;0 \\ (c)\;-\alpha^2 & \quad (d)\;\alpha \end {array}$$