Here's a problem to solve: All planets of the solar system rotate, but not all planets have the same rotational velocity. Which characteristic of a planet is determined by the rotational velocity of the planet?

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

- A: the strength of the gravity
 
- B: the shape of the orbit
 
- C: the size of the planet
 
- D: the length of the day
 