Ana is training for a triathlon, a timed race that combines swimming, biking, and running. While Ana usually practices swimming for two hours per day, she decides to continue for an additional hour because the pool is less crowded than usual today allowing her practice time to be more productive. Which basic principle of individual choice does Valerie's plan illustrate that her husband's advice does not? a. Resources are scarce.
b. All decisions involve opportunity costs.
c. Decisions are made at the margin.
d. People usually exploit opportunities to make themselves better off.

c. Decisions are made at the margin.

Explanation:

It is better to make a trade-off when someone compares the costs with that of  the benefits of doing something. The are called marginal decisions. Making the means comparing its costs as well as its benefits of an activity by doing it a little bit more versus doing a little bit less.

In the context, Ana is making decision at the margin when she decides to practice one hour extra and improve her swimming performance as the event of triathlon is approaching.

Thus, option (d) is correct.

the answer is b hope you pass

anyone below or above ambitious can tell you. so crowns mean brainliest. getting brainliest means your answer needs a good explanation and the person asking the question can understand your answer easily. so say there's a multiple choice question. you don't just want to say your answer is a, hope it . provide evidence and reasoning so that they know that that is the correct answer. a good explanation should have evidence, good reasoning, and your opinion on why you picked that. you don't want to look up their question on the internet and see if you can answer it. pick questions that you 100% know the answer to, so than that way you can provide a better explanation.

best of luck,

the divergent