The organisms listed belong to different animal phyla, representing different stages of evolutionary complexity:
B. Paramecium is a unicellular protist, the least complex.
D. Hydra is a simple multicellular organism belonging to the phylum Cnidaria, with only two primary tissue layers and radial symmetry.
A. Planaria is a flatworm (phylum Platyhelminthes), which is more advanced than hydra as it has three tissue layers (triploblastic), bilateral symmetry, and a centralized nervous system (cephalization).
C. Earthworm belongs to the phylum Annelida. Annelids are more evolutionarily advanced than flatworms because they have a true coelom (body cavity), a closed circulatory system, a segmented body plan, and more complex organ systems.
Based on the analysis above, the correct answer is earthworm - option C
There is an explanation video available below.
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