Answer:
The correct answer is trade-off.
Step-by-step explanation:
The trade-off is a situation in which to increase one thing you need to decrease another. This situation arises because of the scarcity of resources. Since resources are limited we cannot increase spending on everything. To increase spending on one thing we need to give up or decrease spending on others.
Here, time is a fixed resource you can either spend it on a concert or on a birthday. In order to choose one, you have to give up another.