Which situation shows causation
a)when the number of people in a bus increases, the number of animals in a zoo also increases.
b)when the number of hours worked each week by an hourly employee decreases, the amount of money earned by the employee also decreases
C)when the amount of a discount for a sale increases, the number of items sold during the sale decreases
d)when the number of bike trails in a city decreases the amount of rainfall in the city increases