The dog and tapeworm both become ill. The dog becomes ill, and the tapeworm benefits. The tapeworm and dog help each other survive. The tapeworm helps the dog survive.
I gave my students this multiple choice question: Tapeworms live in the intestines of dogs and absorb nutrients from food the dog eats. Which best describes the outcome of this relationship?

Only one answer is correct among these 4 choices:
- The dog and tapeworm both become ill.
- The dog becomes ill, and the tapeworm benefits.
- The tapeworm and dog help each other survive.
- The tapeworm helps the dog survive.

Could you tell me which one is correct?

The dog becomes ill, and the tapeworm benefits.