Write the Nth Term of the Geometric Sequence as a Function

Multiple Choice

Write the nth term of the geometric sequence as a function of n. $a _ { 1 } = 2 , a _ { k + 1 } = 4 a _ { k }$

A) $a _ { n } = 2 ( 4 ) ^ { n - 1 }$
B) $a _ { n } = - 2 + 4 n$
C) $a _ { n } = 2 ( 4 ) ^ { n }$
D) $a _ { n } = 2 \left( \frac { 1 } { 4 } \right) ^ { n - 1 }$
E) $a _ { n } = 4 ( 2 ) ^ { n - 1 }$