[单选题]
A mass attached to the fmdf )m ,.l;o7:oidtrureagci*yd z r3tjc+w3/ 4e end of a spring executes simple harmonic motion according to the eqrwi d3z/3cc+*jtg a4yuation $y = 0.50 \; \sin (18\pi \times t)$ 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. $1/18 \; s$