(c)
If $\ \left| \mathcal{z} \right| = \left| \mathcal{z -}2 \right|\mathcal{\ \Rightarrow \ z +}\overline{\mathcal{z}} = 2$
Also, $\left| \mathcal{z} \right| = \left| \mathcal{z} + 2 \right|\mathcal{\Rightarrow \ z +}\overline{\mathcal{z}} = - 2$
Thus, $\left| \mathcal{z +}\overline{\mathcal{z}} \right| = 2$