The displacement y of a wave travelling in the x-direction is given by $\mathrm{y}={10}^{-4}\sin \mathrm{\hspace{0.17em}\hspace{0.17em}}\left(600\mathrm{t}-2\mathrm{x}+\frac{\mathrm{\pi }}{3}\right)$ metres, where x is expressed in metres and t in seconds. The speed of the wave-motion, in ms^–1, is 

• A

  200

• B

  300

• C

  600

• D

  1200