In levers, Class 2 levers can be used to increase the force that must be applied. In a Class 2 lever, the load is situated between the effort (force applied) and the fulcrum, allowing for a mechanical advantage that increases the applied force.
Therefore, the correct response is:
Class 2 and 3 (although it's primarily Class 2 that provides a mechanical advantage; Class 3 typically does not increase force but allows for increased distance or speed).