Suppose you are designing a heat exchanger to remove energy from a motor as quickly as possible. Energy will be transferred from the motor to the heat exchanger. Then the energy will be transferred from the heat exchanger to the air. The table shows the thermal conductivities of a few substances as measured in W/m·K. The greater the thermal conductivity, the faster the rate of energy transfer. Which material would be the best choice? a: copper
b: glass
c: steel
d: polystyrene