What type of relationship do limpets have with Clathromorphum algae?

A. Mutualistic relationship, where limpets clean the algae's surface and receive food in return
B. Parasitic relationship, where limpets harm the algae for their own benefit
C. Competitive relationship, where limpets compete with the algae for resources
D. Predator-prey relationship, where limpets feed on the algae
Answer: 