The correct option is D Inertia
It’s because of inertia, which is simply the tendency of any body to continue on whatever path it’s travelling unless acted on by an external force. For a standing passenger, his/her body will tend to continue along the straight line route the bus was travelling before the sharp turn. As the passenger’s feet are fairly firmly located to the floor of the bus when it turns, a force will act upon the passenger’s feet accelerating them towards the centre of the turn.