Raphael is training for a triathlon, a timed race that combines swimming, biking, and running. consider the following sentence: raphael has only 20 hours per week that he can devote to training for his race. which basic principle of individual choice does this sentence best illustrate? -all costs are opportunity costs.-resources are scarce.-people usually exploit opportunities to make themselves better off.-many decisions are made on the margin. resources are scarce

Resources are scarce and All costs are opportunity costs.

Explanation:

The scarce resource in this case is time. Because resources are scarce, then people have to take choices strategically. If time was infinite, then Raphael would dedicate more time to train.

The sentence could also illustrate that all costs are opportunity costs. The cost of doing something else, is not training. For example, the cost of the time that he dedicates to study, is the time that he could spent training. But here we are also talking about time, then it could be option A or option B, but for me, A and B are correct.

Because resources are scarce, all of what we decide to do have an opportunity cost.

you have to put the parentheses like this:

in fact, you have to perform the operation inside parentheses first, and then proceed in order: