If $z_1,z_2,z_3,z_4$ are the roots of $z^4=1$, then $\sum\limits_{i=1}^4 z_i^3$=?

Question

$\begin{array}{1 1}(A)4 \\ (B) 0 \\ (C) 1+i \\(D) 1-i \end{array}$