Question 3
One person pushing a bus cannot move it, yet a group pushing together can. Why can one person not move it?
The right answer is the one marked above.
Because the force applied is less than the friction, so the forces balance. The total force on the bus is then zero, so it does not move.
When a group pushes, the force applied overcomes the friction. An unbalanced force is then left over and the bus begins to move.
"No force" and "balanced forces" are not the same thing. Even while one person pushes there are two forces at work — they cancel each other out.