Question

which example best demonstrates positive taxis?
moths attracted to a light
moving towards food
detection using pheromones

Explanation:

Positive taxis is a directed movement towards a favorable stimulus. Moths being attracted to light (phototaxis) is a classic example of positive taxis. Moving towards food can be chemotaxis/geotaxis etc but is a bit more general. Detection using pheromones is more about chemical - sensing and not as direct an example of positive taxis as moths to light.

Answer:

moths attracted to a light