Simplify the Polynomial by Combining Like Terms $$- 15 x ^ { 9 } + 4 x ^ { 6 } + x ^ { 9 } + 6 x ^ { 9 }$$

Multiple Choice

Simplify the polynomial by combining like terms.
- $$- 15 x ^ { 9 } + 4 x ^ { 6 } + x ^ { 9 } + 6 x ^ { 9 }$$

A) $- 4 x 18$
B) $- 8 x ^ { 9 } + 4 x ^ { 6 }$
C) $- 4 x ^ { 9 } - 4 x ^ { 6 }$
D) $- 15 x ^ { 9 } + 4 x ^ { 6 } + x ^ { 9 } + 6 x ^ { 9 }$