Determine the Degree of the Polynomial $- 6 a ^ { 4 } - 14 a ^ { 2 } + 5 a + 7 a ^ { 6 }$

Determine the degree of the polynomial.
- $- 6 a ^ { 4 } - 14 a ^ { 2 } + 5 a + 7 a ^ { 6 }$

A) 6
B) 13
C) 4
D) 12