An insect has primarily muscle attached to the exoskeleton.
striated
circular
longitudinal
smooth

The correct answer is option (A) striated.

An exoskeleton is an external, hard, encasement present on the surface of organisms. Insects show the presence of the characteristic exoskeleton which supports them and protects them from the predators. The muscles of the insects attached to the exoskeleton is primarily of striated type with varying lengths of the structural and functional units responsible for contraction called the sarcomeres. The muscles show high levels of homology with the vertebrate muscles in terms of their structure, protein content, contractility and regulation.

"a.) well–developed vascular system."