When the car turns on a curved road, the passengers sitting in it feel a force on themselves in the opposite direction of the center, this force is due to . . . . . . . .

1. When a car turns on a curved road, the passengers feel a force that appears to push them outward, away from the center of the curve. This force is commonly referred to as centrifugal force.

2. Centrifugal force is not a real force but is rather a perceived force experienced due to the inertia of the passengers. It is the result of the tendency of an object to move in a straight line while the car is changing direction.

3. The sensation of this force is due to the inertia of the passengers' bodies, which want to continue moving in a straight line. As the car turns, the passengers feel pushed to the outside of the curve.

4. The other options are not correct because:

- Inertia is the property of an object to resist changes in its state of motion, but it is not the force that passengers feel.

- Centripetal force is the force that acts towards the center of the curve, keeping the car (and passengers) on the curved path. It is not the force felt by passengers; rather, it is the force responsible for making the turn possible.

- Gravitational force is the force of attraction between objects due to their masses and does not relate to the sensation experienced when turning on a curved road.

Thus, the correct answer is Option A: centrifugal force.