Add or Subtract as Indicated and Simplify If Possible $\frac { 6 } { 9 a ^ { 2 } - b ^ { 2 } } - \frac { 1 } { 3 a ^ { 2 } - a b }$

Multiple Choice

Add or subtract as indicated and simplify if possible.
- $\frac { 6 } { 9 a ^ { 2 } - b ^ { 2 } } - \frac { 1 } { 3 a ^ { 2 } - a b }$

A) $\frac { a + b } { a ( 3 a + b ) }$
B) $\frac { 1 } { a ( 3 a + b ) }$
C) $\frac { 9 a - 3 a - b } { a ( 3 a + b ) ( 3 a - b ) }$
D) $\frac { a } { 3 a + b }$