Two waves are represented by \[{{y}_{1}}=a\sin \left( \omega \,t+\frac{\pi }{6} \right)\] and \[{{y}_{2}}=a\cos \omega \,t\]. What will be their resultant amplitude [RPMT 1996]

• A.            a    
• B.            \[\sqrt{2}\,a\]
• C.            \[\sqrt{3}\,a\]                     
• D.            2a