Beats are produced by two waves given by \[{{y}_{1}}=a\sin 2000\,\pi t\] and \[{{y}_{2}}=a\sin 2008\,\pi t\]. The number of beats heard per second is [CPMT 1990; DCE 1999]

• A.   Zero     
• B.   One
• C.   Four     
• D.   Eight