TOLC-med 2008 electric potential

Two equal and opposite electric charges are at a distance D.
What is the electric potential at the midpoint between the two charges?
A)Double the potential due to each single charge
B) Zero

i thought it would be A)
if they were the same charge there would be repulsion and the potential at the mindpoint would be zero
if they are opposite charges it should be double the potential since the midpoint receives the electric potential of q+/q- and q-/q+

However the answer is B)
What am i not understanding??