What is the main physical characteristic of a nymph?

The main physical characteristic of a nymph is that it resembles the adult form but lacks certain features. Nymphs are the juvenile life stages of certain insects, particularly those that undergo incomplete metamorphosis, such as grasshoppers and dragonflies. Unlike larvae, which can look significantly different from their adult counterparts, nymphs usually closely resemble adults in body shape and size but typically do not have fully developed wings or reproductive organs. This similarity allows nymphs to be better adapted to their environments as they mature.

The other options do not correctly represent the defining features of nymphs. For instance, while some insects may have wings in their adult stage, nymphs typically do not possess wings. Similarly, nymphs are not capable of reproduction like adult insects can. Also, the comment about having a complete exoskeleton does not capture the essence of what differentiates a nymph from an adult; instead, it is the developmental stage and the presence or absence of certain mature features that define them.