Answer the following question given this paragraph: 

Friction is the force that resists motion. In most beginning physics classes, friction is ignored. Concepts can be understood and calculations made assuming friction to be nonexistent. Whenever physics intersects with the real world, however, friction must be taken into account. Friction exists between two touching surfaces because even the smoothest looking surface is quite rough on a microscopic scale.


Q: What type of force exists between two touching surfaces?

 Choices:

- opposing

- centrifugal

- tension

- friction

A:
friction
