Answer: b. gasoline
Step-by-step explanation:
The leaking underground storage tanks have been found as a threat to the groundwater. The gas stations, industries and other entities use underground storage tanks to hold toxic materials like oil, gasoline underground to prevent their exposure to the air as these are flammable and volatile. Other dangerous substances include heavy metals, toluene and benzene. The leakage of these materials can contaminate the groundwater supplies.