Simplify the Expression $\left( x ^ { 4 } \right) ^ { 3 }$

Multiple Choice

Simplify the expression. Assume all variables represent nonzero real numbers.
- $\left( x ^ { 4 } \right) ^ { 3 }$

A) $x ^ { 12 }$
B) $3 x ^ { 4 }$
C) $12 x$
D) $x ^ { 7 }$