Choose the pair in which the words are differently related from the rest.

The correct answer is D. Plasmodium : Cilia.

Cockroaches, lizards, and hydras all have appendages that are used for sensing their environment. Antennae are used by cockroaches to detect movement, smell, and taste. Flagella are used by lizards to move around. Tentacles are used by hydras to capture prey.

Cilia are short, hair-like projections that are used for locomotion and feeding in some organisms. However, Plasmodium is a parasite that does not have cilia. Instead, it has a flagellum that it uses to move around.

Therefore, the pair of words “Plasmodium : Cilia” is the only pair in which the words are not related in the same way as the other pairs.