Which option should the engineers focus on as they develop the train in the following scenario? Richmond, Virginia, has recently approved the construction of a metro system throughout part of the city. As engineers study other metro lines, they notice that there is an extreme amount of energy lost as the trains start and stop.

A) Engineers can design a train with a regenerative braking system.
B) Engineers can design a train involving larger hydraulic power systems.
C) Engineers can design a train with additional valves to increase energy.
D) Engineers can design a train with additional fluid pumps to increase efficiency.