Here's a problem to solve: To keep a heavy box sliding across a carpeted floor at constant speed, a person must continually exert a force on the box. This force is used primarily to overcome which of the following forces?

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

- A: Air resistance
 
- B: The weight of the box
 
- C: The frictional force exerted by the floor on the box
 
- D: The gravitational force exerted by the Earth on the box
 