Which of the following is an example of class 1 flies?

The correct choice is the one that identifies mayflies and caddisflies as examples of class 1 flies. This classification is significant because mayflies and caddisflies belong to the order Ephemeroptera and Trichoptera, respectively, which are both crucial in freshwater ecosystems. They serve as sensitive indicators of water quality and are often used in ecological assessments.

Mayflies have a life cycle that emphasizes clean, oxygen-rich environments, while caddisflies are known for their varied habitats, including flowing streams and lakes. Their presence typically indicates good water quality, making them essential for ecological monitoring.

In contrast, the options that list houseflies and fruit flies, horseflies and blackflies, or fleas and bedbugs would not be classified under class 1 in this context. Houseflies and fruit flies are more associated with terrestrial environments and have different ecological roles. Horseflies and blackflies, while also flies, do not fit the classification for class 1. Fleas and bedbugs are not flies in the traditional sense but rather wingless insects that belong to different orders. Hence, mayflies and caddisflies are the appropriate representatives of class 1 flies within the context of water quality assessment and ecological importance.