The rate of heat transfer between an electric motor and its surroundings is given bye-t - 1.where t is in seconds and Q is in kW. The shaft of the motor rotates at a speed of 200 rad/s and applies a torque of 20 N-m on the load. The motor draws a constant electrical power input of 5 kW. The time rate of change of energy (kW) of the motor is given by:

• A. e-t
• B. 1 + e-t
• C. 1 - e-t
• D. 2 + e-t