If \[y=A\cos nx+B\sin nx,\] then \[\frac{{{d}^{2}}y}{d{{x}^{2}}}=\] [Karnataka CET 1996]

• A.            \[{{n}^{2}}y\]                       
• B.            \[-y\]
• C.            \[-{{n}^{2}}y\]
• D.            None of these