Find the Sum or Difference $\left( - 2 m ^ { 2 } \right) \left( 4 m ^ { 3 } \right)$

Multiple Choice

Find the sum or difference.
- $\left( - 2 m ^ { 2 } \right) \left( 4 m ^ { 3 } \right)$

A) $8 \mathrm {~m}$
B) $- 8 m ^ { 5 }$
C) $8 m ^ { 6 }$
D) $- 8 m$