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

Ans. A

The force is everywhere

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

1. Yes
2. No

Ans. What do you mean by contact? Does exchanging photons/gravitons count as contact? On a more practical level, it is helpful to remember, "no contact, no force except gravity, in most problems of classical mechanics".

The work energy “theorem”

The work energy theorem, $\Delta T = W$ where $T$ is the kinetic energy (and $\Delta T = T_2 - T_1$ is its change) and $W$ is the net work done on the particle, is

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