The equation of a progressive wave is given by 
  $\mathrm{y}=\mathrm{asin}(628\mathrm{t}-31.4\mathrm{x})$
If the distances are expressed in cms and time in seconds, then the wave velocity will be 

• A

  314 cm/sec

• B

  628 cm/sec

• C

  20 cm/sec

• D

  400 cm/sec