Question: Emily is riding her bicycle. Which best explains why only some of the energy used to pedal her bicycle is transferred into forward motion of the bicycle?

  Options: 
 A. The energy of the bicycle tire is applied in a circular motion.
 B. The energy of the bicycle is transferred to only one wheel.
 C. The gears and chain of the bicycle are covered with oil.
 D. The gears and chain of the bicycle generate friction. 
Answer: D