Here's a problem to solve: 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?

Among the 4 following options, which is the correct answer?

- 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.
 