Here's a problem to solve: Collars that emit radio waves are sometimes placed on animals to find their location. Which is the best reason for using radio waves as a method of tracking the animals?

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

- A: Radio waves are visible.
 
- B: Radio waves have a high frequency.
 
- C: Radio waves spread in all directions.
 
- D: Radio waves are created by the animal.
 