Warm-Up 3/29: Causation (A.4B)

When the amount of a discount for a sale increases, the number of items sold during the sale decreases.

When the number of hours worked each week by an hourly employee decreases, the amount of money earned by the employee also decreases.

When the number of people in a bus increases, the number of animals in a zoo also increases.

When the number of bike trails in a city decreases, the amount of rainfall in the city increases.

Which situation shows causation?