Which pair of variables shows a clear causal link? a person's academic degree and state of birththe cost of aviation fuel and flight durationthe number of lights switched on in a room and the room's brightness a person's annual income and the type of pet owned

The correct answer should be number of lights switched on in a room and the room's brightness

As you turn on more lights, the room gets brighter. Other options are not it because state of birth does not cause you to have higher or lower degrees innately, while the cost of fuel will not be affected by the flight duration. You will pay more for the amount of fuel, but the price of a single gallon would not change. Pets and annual income have nothing in common.