If $$ \left(\frac{p^{-1}   q^2}{p^3   q^{-2}}\right)  + \left(\frac{p^{5}   q^{-3}}{p^{-2}   q^{3}}\right)^\frac{1}{3}  = p^a  q^b $$, then the value of a + b, where p and q are different positive primes, is

A

1

B

2

C

0

D

-1