Find a Formula for the Nth Term of the Sequence $0 , - 1,0,1,0 , - 1,0,1 ( 0 , - 1,0,1$

Multiple Choice

Find a formula for the nth term of the sequence.
- $0 , - 1,0,1,0 , - 1,0,1 ( 0 , - 1,0,1$ repeated)

A) $a _ { n } = \cos \left( \frac { \mathrm { n } \pi } { 2 } \right)$
B) $a _ { n } = \sin ( n \pi )$
C) $a _ { n } = \sin \left( \frac { \mathrm { n } \pi } { 2 } \right)$
D) $a _ { n } = \cos ( n \pi )$