We are standing in a stationary bus. When the bus suddenly starts,why are we thrown in the backward direction?

(N/A) When we are standing in a stationary bus,our feet are in contact with the floor. There is a frictional force between our feet and the floor of the bus.
When the bus suddenly starts,due to friction,our feet start moving in the direction of the bus,whereas the rest of our body tries to retain its position due to inertia of rest.
Hence,we are thrown in the backward direction,which is opposite to the direction of the acceleration of the bus.