Concept:Organization complexity increases from simple multicellular animals to advanced vertebrates.
Explanation:Hydra (I) is a simple multicellular organism with tissue-level organisation.
Snail (IV) is a more complex invertebrate with organ systems.
Snake (III) is a vertebrate with a higher structural complexity.
Owl (II) is a bird, having the most advanced body systems among the given organisms.
Therefore, the increasing order is Hydra → Snail → Snake → Owl.
Answer:I, IV, III, II, which is option B.