Multiply Assume That All Variables Represent Natural Numbers $- 9 k ^ { r + 1 } \left( 7 k ^ { r + 4 } - 4 k ^ { r + 3 } - 6 k \right)$

Multiple Choice

Multiply. Assume that all variables represent natural numbers.
- $- 9 k ^ { r + 1 } \left( 7 k ^ { r + 4 } - 4 k ^ { r + 3 } - 6 k \right)$

A) $- 63 k ^ { r + 5 } + 36 k ^ { r + 4 } + 54 k ^ { r + 1 }$
B) $- 63 k ^ { r + 5 }+ 36 k ^ { r + 4 } + 54 k ^ { r + 2}$
C) $- 63 k ^ { 2 r + 5 } + 36 k ^ { 2 r + 4 } + 54 k ^ { r + 1 }$
D) $- 63 k ^ { 2 r + 5 } + 36 k ^ { 2 r + 4 } + 54 k ^ { r + 2 }$