For ordinary terrestrial experiments,which of the following observers is inertial?

We are standing in a bus moving with constant velocity. When brakes are applied to the bus,we are thrown in the forward direction. Why?

$A$ rider on horseback falls when the horse starts running all of a sudden because:

An aircraft is moving with a velocity of $300\,m/s$. If all the forces acting on it are balanced,then:

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R.$
Assertion $A:$ An electric fan continues to rotate for some time after the current is switched off.
Reason $R:$ The fan continues to rotate due to inertia of motion.
In the light of the above statements,choose the most appropriate answer from the options given below.

$Assertion$ : The driver in a vehicle moving with a constant speed on a straight road is an inertial frame of reference.
$Reason$ : $A$ reference frame in which Newton's laws of motion are applicable is non-inertial.