$.$ Suppose future technology can realize a deep tunnel for bullet trains under the Pacific Ocean, linking China and the United States. If air resistance and rail friction can be minimized, which of the following statements must be false? A$.$ The train can utilize Earth$$s gravity for acceleration and deceleration B$.$ The train can use less energy compared to traveling on the surface C$.$ The gravitational potential energy of the train is lower on the surface than at the deepest point in the tunnel D$.$ Theoretically, the train can execute an oscillatory motion between the two ends of the tunnel E$.$ The weight of the train can vary over the course of travel