Perform the Indicated Operation and Write Your Answer with Positive $$\frac { ( \mathrm { mn } ) ^ { - 1 } } { \mathrm {~m} ^ { - 2 } + \mathrm { n } ^ { - 2 } }$$

Multiple Choice

Perform the indicated operation and write your answer with positive integer exponents.
- $$\frac { ( \mathrm { mn } ) ^ { - 1 } } { \mathrm {~m} ^ { - 2 } + \mathrm { n } ^ { - 2 } }$$

A) $\frac { m n } { n + m }$
B) $\frac { n } { n ^ { 2 } - m ^ { 2 } }$
C) $\frac { m ^ { 2 } + n ^ { 2 } } { m n }$
D) $\frac { m n } { n ^ { 2 } + m ^ { 2 } }$