The displacement $y$ of wave travelling in the $x$ -direction is given by $y=10^{-4}\sin (600t-2x+\pi /3)$ metres, where $x$ is in metres and $t$ in seconds. The speed of the wave-motion in $\text{m/s}$ is:

1. A
   $300$
2. B
   $600$
3. C
   $1200$
4. D
   $200$