Answer:
the park
Step-by-step explanation:
An opportunity cost is any opportunity that you are giving up in order to chase another opportunity. In this case, the city chose to build an office building, in doing so they gave up the opportunity to build a park with that money. Therefore, the opportunity cost in this scenario would be the park. This is assuming that the resources are only enough for one of the two options, otherwise, if the city is able to complete both builds (the office and the park) then there would be no opportunity cost because they are not giving up anything.