The equilibrium position is that at which the pendulum is at its lowest point; it is called this because, absent any other forces acting upon it, this is the point at which the pendulum would be at a stable, motionless equilibrium. It is also the point at which the pendulum, having been released from above, has translated its starting gravitational potential energy fully into kinetic energy. As such, this means that at this point the pendulum is at its maximum D) velocity.
