Which of these animals undergoes incomplete metamorphosis?
a) beetles
b) butterflies
c) praying mantis
d) moths

C). praying mantis

The life cycle of insects that undergo incomplete metamorphosis takes place in three stages: egg, nymph and adult. When the eggs are hatched then the insect body undergo several nymphal stages to develop into an adult form. The adult insect can be distinguished from the nymphs by size and presence of wings. The animal which undergoes incomplete metamorphosis is praying mantis.

"a.) well–developed vascular system."

well the answer is 2!