The correct answer is A. current meter.
A current meter is an instrument used to measure the speed of water flow. It is typically used in rivers, streams, and other bodies of water to measure the flow rate. Current meters can be either mechanical or electronic. Mechanical current meters use a propeller or vane to measure the speed of the water, while electronic current meters use a sensor to measure the change in electrical current caused by the water flow.
A venturimeter is a device used to measure the flow rate of a fluid. It consists of a narrow section (throat) in a pipe, with a larger section (inlet) and a larger section (outlet) on either side. The pressure difference between the inlet and outlet is measured, and this can be used to calculate the flow rate.
A pitot tube is a device used to measure the velocity of a fluid. It consists of a tube with a small opening facing the oncoming fluid. The pressure difference between the inside and outside of the tube is measured, and this can be used to calculate the velocity of the fluid.
A hotwire anemometer is a device used to measure the speed of air flow. It consists of a thin wire that is heated by an electric current. The rate at which the wire cools is proportional to the speed of the air flow.
In conclusion, the correct answer is A. current meter.