mutualism commensalism parasitism phototropism
I gave my students this multiple choice question: A plover bird eats bits of food that become stuck in a crocodile's teeth without being hurt. The crocodile gets its teeth cleaned and the bird gets food. Which type of relationship exists between the bird and the crocodile?

Only one answer is correct among these 4 choices:
- mutualism
- commensalism
- parasitism
- phototropism

Could you tell me which one is correct?

mutualism