As the pendulum swings from position A to position B, the potential energy decreases while the kinetic energy increases. According to the law of conservation of energy, the total energy in a system remains constant, neglecting friction. Therefore, the potential energy lost by the pendulum is converted into kinetic energy. The correct relationship of kinetic energy to potential energy as the pendulum swings from position A to position B is:
The potential energy decrease is equal to the kinetic energy increase.
So, the answer is option B.