Concept:The instrument shown is an anemometer.
It measures the speed of the wind.
Explanation:An anemometer has rotating cups that turn when the wind blows.
The faster the wind blows, the faster the cups rotate.
This rotation is converted into a wind-speed reading.
A barometer measures atmospheric pressure.
A hygrometer measures relative humidity.
A wind vane indicates wind direction.
Therefore, the instrument in the diagram is used to measure the speed of the wind.
Answer:D. speed of wind
