When a bus moves forward after stopping to pick up passengers, why do the passengers feel as though they are being pushed back against their seats?

a. the passengers' bodies tend to remain still relative to the ground while the bus is moving.

b. the forward force caused by the inertia of the bus pushes back on the passengers' bodies.

c. the force of gravity tries to hold the bodies of the passengers in place.

d. the body of the bus moves faster than the seats on the bus due to inertial forces.