Answer:
1) The cost of something is what you give up to get it
Explanation:
As it can be seen that for opting one service the person should leave the other activity that we called as an opportunity cost
In the given situation, since it is mentioned that Janet can earn $10 per hour and for pool she has to pay $4 as an entrance fee
So here the sacrifice is made with respect if one activity is selected
Therefore the option 1 is correct