The correct answer is C. anemometer.
A speedometer measures the speed of a vehicle. A tachometer measures the rotational speed of an engine or other rotating machine. An audiometer measures the hearing acuity of a person. An anemometer measures the speed of wind.
An anemometer is a device used for measuring wind speed and direction. It is typically used in meteorology, aviation, and other fields where wind speed and direction are important. There are many different types of anemometers, but the most common type is the cup anemometer. A cup anemometer consists of three or four cups mounted on a vertical rod. The cups are spun by the wind, and the rotation of the cups is measured by a counter. The speed of the wind is then calculated from the number of revolutions of the cups per minute.
Anemometers are important tools for measuring wind speed and direction. They are used in a variety of applications, including meteorology, aviation, and wind energy.