Answer:- A.

The input is d.
Step-to-step explanation:-
If 'c' represents the amount of compost produced in 'd' day from yard waste.
Since, the amount of compost produced in one day =12 pounds
Then the compost produce in d days is given by :

Hence, the function represents the relationship between the amount of compost and the number of days is given by :-

Since, 'c' is dependent variable which depends on the number of days 'd'.
Therefore, the input is d.