How are algae and polyps related?

The polyps receive carbon dioxide from the algae
the polyps get most of their food from the algae
The polyps receive shelter from the algae
The polyps embed themselves in the flesh of the algae

Algae and polyps have a mutualistic relationship where the polyps provide shelter and nutrients for the algae, while the algae provide the polyps with food through photosynthesis. This close relationship allows both organisms to thrive in their environment.