In many cities, firms that own office buildings can renovate them for use as residential apartments. according to a news story, in many cities "residential rents are surpassing office rents." source: eliot brown, "developers turn former office buildings into high-end apartments," wall street journal, may 7, 2014. the response to an increase in residential rents would be

A decrease in the supply of office space, shifting supply to the left.

Explanation:

A decrease in supply can take place as shift to the left or upwards in a supply curve. In this case, a left shift indicates that, in the time that the supply of office space decreases, firms that own office buildings produce and sell a smaller amount at every price. The upward shift shows that supply usually decreases when the production costs increase, so producers must set a higher price than in the past to supply an established quantity of output.

the answer is a. or c.