Concept:Wind direction is the direction from which the wind blows, and it is measured using a wind vane.Explanation:A wind vane rotates freely on a fixed rod and points toward the direction the wind is coming from.An anemometer measures wind speed, not wind direction.A Secchi disc is used to measure water clarity or turbidity.A slope gauge is used to measure the angle or gradient of a slope.Therefore, the ecological instrument for measuring wind direction is the wind vane.Answer:B. wind vane