How can knowing the opportunity cost of buying a product affect people's economic decisions?
A)
It can lead them to consider the ways in which buying the product supports a flawed
and unjust economic system.
B)
It can show them how to avoid a trade-off and use the same resources to meet two
needs rather than one,
C)
It can force them to recognize how the decision they are about to make compares to all
other possible decisions.
D)
It can help them to prioritize two possible uses of their money and guide them to
choose the best option.

C. It can force them to recognize how the decision they are about to make compares to all  other possible decisions.

Explanation:

Opportunity cost refers to the expenses or sacrifices that might incurred when we choose a certain decision over another.

When making an economic decision, Opportunity cost will show the people the monetary loses and gain that might incurred from all possible options that they have.  With this information, people could choose the decision that give them the most benefit/

For example:

Let's say that Stella has 5 hours of free time during the day. She has the options to do a 4-hour part time job that will make her earn $15/hour.  But, let's say that Stella choose to use that 5 hours to play games with her phone rather than doing the part-time job. In such situation, an opportunity cost of a $60 per day just incurred because of Stella's decision.

the national congress's powers over the states were specific and definite: it had the sole power to negotiate treaties, declare war, and make peace. all powers not granted to congress were reserved for state governments. congress had no power to levy taxes, for example.