If $z_{1}, z_{2}$ and $z_{3}$ are complex numbers such that $\left|z_{1}\right|=\left|z_{2}\right|=\left|z_{3}\right|=1$ and $z_{1}+z_{2}+z_{3}=0$, then $\left|\frac{1}{z_{1}}+\frac{1}{z_{2}}+\frac{1}{z_{3}}\right|$ is
(a) equal to 0
(b) equal to 1
(c) greater than 1 and less than 3
(d) equal to 3