The displacement y of a wave travelling in the $x$-direction is given by <br> $y = 10^{-4} \sin (600 t - 2x + \frac{x}{3})$ metre, <br> where, $x$ is epressed in metres and $t$ in seconds. The speed of the wave-motion, in $ms^{-1}$ is :

Question

( A ) 300
( B ) 600
( C ) 1200
( D ) 200