Which pair is correct?

Answer: (c) House fly, Dragon fly, Butterfly

Housefly, dragonfly and butterfly are all insects.

The idea

A name is not a classification. Check what each animal really is, and only one group has three members of the same kind.

Sea horse → fish; sea cucumber and sea urchin → echinoderms → Starfish → echinoderm; cuttlefish → mollusc → Housefly, dragonfly, butterfly → all insects → Earthworm and tapeworm → worms; ringworm → a fungal skin disease

Why the others are wrong

(a) The sea horse is a fish; sea cucumbers and urchins are echinoderms.

(b) Starfish (echinoderm), cuttlefish (mollusc) and dog (mammal) are unrelated.

(d) Ringworm is a fungal skin infection, not a worm.

The trap

(d) has three “worms” — but ringworm is a fungus.

Also know

Insects have a head, thorax and abdomen, with three pairs of legs. Spiders and scorpions are arachnids with four pairs of legs; both groups are arthropods. Octopus and squid are molluscs. Earthworms are segmented annelids, while tapeworms are flatworms. Adult echinoderms usually have a five-part body pattern and a water vascular system for movement.