A.\(f = \frac{1}{{2\pi }}\sqrt {\frac{m}{k}} \).
B.\(f = \frac{1}{{2\pi }}\sqrt {\frac{k}{m}} \).
C.\(f = 2\pi \sqrt {\frac{k}{m}} \).
D.\(f = 2\pi \sqrt {\frac{m}{k}} \).