State the Period of the Function:​ $y = - 3 \sec \frac { \pi x } { 3 }$

Multiple Choice

State the period of the function:​ $y = - 3 \sec \frac { \pi x } { 3 }$ ​

A) ​ $\frac { \pi } { 3 }$
B) 6
C) 8
D) $6 \pi$
E) 12