Final answer:
The sentence where 'current' means 'a flow of electricity' is B. Before installing the ceiling fan, David turned off the current.
Step-by-step explanation:
The sentence where 'current' means 'a flow of electricity' is B. Before installing the ceiling fan, David turned off the current. In this sentence, 'current' refers to the flow of electricity through an electrical circuit. Turning off the current means cutting off the flow of electricity to the ceiling fan.