Operation of buses is prohibited if:

Explanation

In both cases; a bus must have at least two wheel chocks and two fire extinguishers.

For a bus, both the wheel chocks and the fire extinguishers must number at least two; so having only one of each is just as much an offence as having none. This point is more a matter of memory than of engineering, and the exam counts on exactly that: the options are worded so that you translate "there is one" into "so there is no problem".

The logic of the number two is separate in each case. Chocks must be placed on both sides or under two wheels so as to restrain the vehicle against movement in both directions; a single chock only prevents rolling one way and is not enough on a real gradient. With extinguishers the issue is access: on a bus, one extinguisher must be within the driver's reach and the other in the passenger compartment, because a fire may start in the engine or in the compartment, and an extinguisher trapped behind the flames effectively does not exist. Besides which, one extinguisher may be empty or faulty, and in a fire there is no opportunity to try again.

Keep these figures together: a bus needs two wheel chocks, two fire extinguishers, a first-aid kit and an emergency stop sign. Any shortfall on this list prohibits the bus from moving.

• One wheel chock is not enough and that shortfall is an offence, but choosing it alone ignores the shortfall in extinguishers. • One fire extinguisher is also below the required number, but it is not the only fault raised in the question and leaves the answer incomplete.

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