To save fuel, what should you do?

To save fuel, what should you do?
A)Drive at 90 kilometers per hour, always.
B)Adapt the gears to the vehicle's needs.Correct
C)Drive in low gears.
Proper gear management is one of the key aspects of efficient driving.
Driving in higher gears and at low engine revs results in lower fuel consumption.
We should use the highest gear possible (4th or 5th), even in the city, and keep the engine running at low revs.
With lower gears, since the engine runs at higher revs, it will consume more fuel.