[单选题]
A simple pendulum executing simple harmonic motion is release cnvk35qgiw j-)8 /+) dcyrptsd from one end ag-f4ks*he ,le nd reaches equilibrium ph k,4es-eg*fl osition in $2\,s$. Just after the equilibrium position, the length of the pendulum is reduced to one-fourth of its initial value because of wrapping around a nail.
