[单选题]
A simple pendulum executing simple harmonic moth h 37:/po9vfyv;gzk tio:ofn pt+a wz xxc,*s :/v/v8vyn is released from one end and reaches equilibriuszy c,t:xn +/wp vvox:8f/av*m position 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.
