Opportunity cost means that something needs to be (B) given up.
Opportunity cost happens when you desire to buy 2 items but you can only afford to pay for 1. The value of the opportunity cost will be the value of the item you have to forgo or give up.
For example, you want to buy jeans and a jacket. Jeans costs $20 while the jacket costs $25. You only have $30. So, you can only buy one item. If you buy the jeans, you opportunity cost is 25 for the jacket. If you buy the jacket, your opportunity cost is 20 for the jeans.
