Gaseous exchange in an insect

The Spiracles is/are used for gaseous exchange in insects.

Explanation:

The Spiracles is a respiratory structure or an opening found on the exoskeleton of insects. It acts as a medium of gaseous exchange not only for Insects (Insecta) but also for some Arachnid (spiders and others).

stress fractures occur largely in the feet and legs and are common in sports that require repetitive impact, primarily running/jumping sports such as gymnastics or track and field.

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".