[单选题]
A simple pendulum executing s-1w .mskcyafzj*::i w+vc t b+g),x hoimple harmonic motion is released from onmbz6aa+urd74lrr 8 1ue end and reaches equilibrium position8+46dr auuz 1arb7mr l 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.
