You are a scientist who notices great similarity between the spines of a hedgehog and the spines of a porcupine. when you study their genetics, however, you notice that the set of genes that code for hedgehog spines is a different set of genes than the set that codes for porcupine spines. you decide this must be an example of

Analogous structures I think

plato users:

d.  

there was a variety of food available on island x, but there were only large seeds and nuts on island y.

these muscles maintain the blood pressure in the vessels. the smooth muscles are innervated by nerves of the autonomic nervous system. when the muscles contract, they cause vasoconstriction of the vessels and increase blood pressure. when the muscles relax, they enable vasodilation of the   blood vessels hence reduce blood pressure.