Which pair of variables has a clear causal link between the two named variables?

A.

the number of hats sold and the number of mittens sold in a city

B.

the amount of butter and the amount of bread consumed by a family

C.

the number of notebooks sold and the number of pens sold in a stationery store

D.

the number of air conditioners sold per day in a city and the daily temperature

E.

the number of hours a person can swim and the depth of the pool

D. the number of air conditioners sold per day in a city and the daily temperature

Step-by-step explanation:

Let analyse all the possible answers:

A. the number of hats sold and the number of mittens sold in a city

They show no relationship towards each other, both of them are independent variables. If you buy hats, you can buy mittens or not it is ok.

B. the amount of butter and the amount of bread consumed by a family

They show no relationship towards each other, both of them are independent variables. If you buy bread, you can eat it with jams, without butter is fine.

C. the number of notebooks sold and the number of pens sold in a stationery store

They show no relationship towards each other, both of them are independent variables. I can use pencil to write on that notebooks, do not need to buy pens.

D. the number of air conditioners sold per day in a city and the daily temperature

They show a strong relationship towards each other, the daily temperature is the independent variable and it makes people want to buy air conditioners (dependent variable)

E. the number of hours a person can swim and the depth of the pool

They show no relationship towards each other, both of them are independent variables. The number of hours a person can swim depends on their ability.

So we choose D.

D. The numbers of notebooks sold and the number of pens sold in a stationery store