Answer:
"However, there was no water to fight it since the water mains had been ruptured by the quake."
Step-by-step explanation:
The sentence from the paragraph that uses a cause-and-effect structure is this one. In this example, the author explains that there was an incident: the water mains had been ruptured by the quake. This is the "cause." Moreover, this cause led to an effect. The effect is that there was no water to fight the fire. Cause-and-effect is one of the most common and useful types of structures.