Out of the following statements.

(A) : Three charge system can't have zero mutual potential energy.

(B) : The mutual potential energy of a system of charges in only due to positive charges.   

Mutual potential energy of a system of charges is given by 

$\sum _{ }\frac{{\mathrm{q}}_{\mathrm{i}}{\mathrm{q}}_{\mathrm{j}}}{{\mathrm{r}}_{\mathrm{i}}{\mathrm{r}}_{\mathrm{j}}}$

Here the sum can be made zero if the charges have opposite signs. 

The sign of the charges will determine the sign of the potential energy and both positive and negative charges contribute to the potential energy.