[单选题]
A mass attached to the free end okng+5y 1 gzdlp35 mox,f a spring executes simple harmonic motion + y+m iz*p*nbeaccording to the equa+*+pzyni e*bmtion $y = 0.50 \; \sin (18\pi \times t)$ where y is in meters and t is seconds. What is the period of vibration?
A. $9.0 \; s$
B. $18 \; s$
C. $1/9 \; s$
D. $1/18 \; s$
