The correct answer is A) a positive displacement pump. Positive displacement pumps are more effective for tank stripping because they can generate higher suction pressures and flow rates compared to other pump types, allowing them to efficiently remove residual fuel and liquids from the bottom of storage tanks. The high suction capabilities of positive displacement pumps make them well-suited for this application, where complete tank drainage is required. In contrast, the other options would not be as effective for tank stripping. Multistage centrifugal pumps (B) generally have lower suction capabilities, the load on top system (C) relies on gravity rather than active pumping, and the water displacement method (D) involves replacing the liquid content with water rather than actively removing it.