Simplify the Expression $- \sqrt { 49 x ^ { 8 } }$

Multiple Choice

Simplify the expression.
- $- \sqrt { 49 x ^ { 8 } }$

A) $\left| 7 x ^ { 4 } \right|$
B) $- \left| 49 x ^ { 4 } \right|$
C) $- 7 x ^ { 8 }$
D) $- \left| 7 x ^ { 4 } \right|$