The correct answer is D. measuring flow of a fluid.
A Venturi tube is a device used to measure the flow of a fluid. It consists of a narrow constriction in a pipe, with a pressure gauge before and after the constriction. The pressure difference between the two gauges can be used to calculate the flow rate of the fluid.
Option A is incorrect because a Venturi tube is not used to measure the intensity of earthquakes. The intensity of an earthquake is measured using the Richter magnitude scale or the Mercalli intensity scale.
Option B is incorrect because a Venturi tube is not used to measure specific gravity. Specific gravity is the ratio of the density of a substance to the density of water. It is measured using a hydrometer.
Option C is incorrect because a Venturi tube is not used to measure density. Density is the mass of a substance per unit volume. It is measured using a balance or a density meter.