The equation of motion for a spring-mass system excited by a harmonic force is\(M\ddot x + kx = F\cos \left( {\omega t} \right),\)Where M is the mass, K is the spring stiffness, F is the force amplitude and ω is the angular frequency of excitation. Resonance occurs when ω is equal to

• A. \(\sqrt {\frac{M}{k}}\)
• B. \(\frac{1}{{2\pi }}\sqrt {\frac{k}{M}}\)
• C. \(2\pi \sqrt {\frac{k}{M}}\)
• D. \(\sqrt {\frac{k}{M}}\)