Find the Square Root $\sqrt { 81 x ^ { 8 } }$

Multiple Choice

Find the square root. Assume that all variables represent positive real numbers.
- $\sqrt { 81 x ^ { 8 } }$

A) $9 x ^ { 2 }$
B) $9 x ^ { 4 }$
C) $9 x ^ { 8 }$
D) $81 x ^ { 4 }$