Which force?

Friction, air resistance, tension, spring force, normal force, etc. are all due to

1. Gravitational force
2. Electromagnetic force
3. Strong force
4. Weak force

The force is everywhere

When two objects exchange forces, they can do so without having to contact each other.

1. Yes
2. No

The work energy “theorem”

The work energy theorem, $\Delta K = W$ where $K$ is the kinetic energy and $W$ is the net work one on the particle, is

1. always valid (in classical mechanics).
2. valid only for conservative forces.