A Fundamental Physical Reason for the Bicycle's High Efficiency as a Transportation

Multiple Choice

A fundamental physical reason for the bicycle's high efficiency as a transportation device is

A) it is a wheeled vehicle.
B) it is not a heat engine.
C) Both of the above.
D) it is a heat engine, but one that does not burn fossil fuels.
E) Nonsense, trains and airplanes are actually more efficient than bicycles.