The correct answer is D. gas velocities.
A hot wire anemometer is an instrument used to measure the velocity of a fluid. It works by heating a wire and measuring the rate at which it cools due to the flow of the fluid. The faster the fluid flows, the more the wire cools. The hot wire anemometer can be used to measure the velocity of gases or liquids.
Option A is incorrect because a hot wire anemometer is not used to measure pressure in gases. A pressure gauge is used to measure pressure.
Option B is incorrect because a hot wire anemometer is not used to measure liquid discharge. A flow meter is used to measure liquid discharge.
Option C is incorrect because a hot wire anemometer is not used to measure pressure in liquids. A pressure gauge is used to measure pressure.