Find a Formula for the Nth Term of the Sequence $- 3,6 , - 9,12 , \ldots$

Find a formula for the nth term of the sequence. $- 3,6 , - 9,12 , \ldots$

A) $a _ { n } = ( - 1 ) ^ { n } 3 n$
B) $a _ { n } = ( - 1 ) ^ { n + 1 } 3 n$
C) $a _ { n } = ( - 1 ) ^ { n + 1 } 3 ^ { n }$
D) $a _ { n } = ( - 1 ) ^ { n } 3 ^ { n }$