Simplify the Expression $$\sqrt [ 4 ] { 16 a ^ { 4 } }$$

Multiple Choice

Simplify the expression. Assume all variables represent positive real numbers.
- $$\sqrt [ 4 ] { 16 a ^ { 4 } }$$

A) $2 a ^ { 2 }$
B) $2 a$
C) $16 a$
D) $2 \sqrt { a }$