Here's a problem to solve: A 20 N object is placed on a surface and starts to slide. What is the most likely reason the object begins to move?

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

- A: Gravity exerts a balanced force on the object.
 
- B: An unbalanced force causes acceleration.
 
- C: Friction is applied to the object.
 
- D: The forces acting on the object are in equilibrium.
 