Final answer:
The correct representation is an exponential curve.
Step-by-step explanation:
The correct representation of the relationship between the amount of plant food remaining (f(x)) and the number of days that have passed (x) based on the given data is D) An exponential curve. In an exponential growth model, the amount of plant food remaining decreases at an increasingly faster rate over time. This is represented by a curve that starts out gradually decreasing and then becomes steeper as time goes on.