Which of the following equation does not represent a simple harmonic motion [Kerala (Med.) 2002]

• A.            \[y=a\sin \omega \,t\]     
• B.            \[y=a\cos \omega \,t\]
• C.            \[y=a\sin \omega \,t+b\cos \omega \,t\]                   
• D.            \[y=a\tan \omega \,t\]