Final answer:
Firefighters are most likely to encounter inoperative standpipes and sprinkler systems in buildings under demolition.
Step-by-step explanation:
Firefighters are most likely to encounter inoperative standpipes and sprinkler systems in c. Buildings under demolition. When buildings are being demolished, the utilities including the standpipes and sprinkler systems may no longer be functional. The demolition process can damage or disconnect these systems, leaving them inoperative.