Before the car starts, the driver and all the passengers should always:
adjust the position of their seats
buckle and adjust their seatbelts
turn on the radio
none of the above

buckle and adjust their seat belts

Explanation:

As we know that inertia is the property of mass due to which an object has tendency to oppose to change its state of motion.

Which we can say that object will all continue its state of motion until and unless some external force will act on it.

So here before starting the car our state of motion is REST and after starting the car we will be in motion so here due to inertia we may have change in state of motion on our body.

So in order to save our-self from change in state of motion we need to hold our body by seat belts so that we can transfer the momentum to the belt.

So here correct answer will be

buckle and adjust their seat belts