Final answer:
The function representing the cost of Ana Lucia renting a car for $20 a day is C(d) = 20d, which is a linear function showing the total cost for any number of days rented.
Step-by-step explanation:
The question relates to creating a function representation of a real-world situation involving renting a car. To match the verbal description 'Ana Lucia rents a car for $20 a day' with its corresponding function representation, one needs to understand the concept of a linear function, which is a mathematical model to describe a constant rate of change. In this case, the cost (C) of renting a car for a certain number of days (d) can be represented as C(d) = 20d. This function tells us that for every day Ana Lucia rents the car, the total cost increases by $20.