Answer:
a. the opportunity cost of buying sweaters decreases.
c. the opportunity cost of buying shirts increases
Explanation:
Opportunity cost is the cost of the next best option forgone when one alternative is chosen over other alternatives.
Let us assume that the price of sweater is $20 and the price of shirt is $10. If the price of sweater increases to $30, the opportunity cost of buying sweater decreases from 10 /20 = 0.5 to 10 / 30 = 0.33.
The opportunity cost of shirt would increase from 20 / 10 = 2 to 30 / 10 = 3.
I hope my answer helps you.