Concept:A Secchi disc is a simple aquatic instrument used to measure water transparency or turbidity.
Explanation:The diagram shows a circular disc attached to a rope or line.
The disc is lowered into the water until it disappears from view.
The depth at which it disappears indicates the clarity of the water.
This helps in studying the light penetration and productivity of an aquatic habitat.
A wind vane measures wind direction.
A six's thermometer measures maximum and minimum temperature.
A hygrometer measures humidity.
Only the Secchi disc matches the instrument shown in the diagram.
Answer:C. secchi disc
