If $z_r(r=1,2,......7)$ are the roots of $(z_r+1)^7+z_r^7=0$, then $\sum\limits_{r=1}^{7} Re(z_r)=?$

Question

$\begin{array}{1 1}(A)0 \\ (B) \large\frac{3}{2} \\ (C) \large\frac{7}{2} \\(D) \large\frac{-7}{2} \end{array}$