Answer:
Mutualism
Step-by-step explanation:
In Commensalism, one organism benefits, while the other neither is helped or harmed.
In Competition, only one organism benefits because only one gets what they are fighting over.
In Parasitism, one organism is helped, while the other is harmed.
In Mutualism, both organisms are helped.
Hope this helps and please correct me if I am wrong. This was the correct answer on Edge! :)