My answer would be radiation.
The correct option is C.
if two organisms are in the same class then they will be in the same phylum. The biological classification hierarchy is arranged in such a way that, two organisms who belong to a lower division on the hierarchy will automatically be in the same group in the higher division.
The arrangement from the smallest to largest hierarchy is this: specie, genus, family, order, class, phylum and kingdom.
Answer:
They are small enough to fit through narrow vessels, have a thin membrane as well as a concave shape, allowing them to absorb gases like oxygen and such very easily.
