The correct option is A Mutualism
Lichens are formed by the symbiotic interaction between algae and fungi which is mutually beneficial to each other. Algae are autotrophic and prepare food for fungi and fungi being heterotrophic, provide shelter and absorb mineral nutrients and
water for its partner. This type of symbiotic interaction in which both the organisms benefit from each other is called mutualism.
Parasitism is a type of interaction between two organisms, in which one organism(parasites) benefit from the other (host), while the host is negatively affected.
Commensalism is a type of interaction between two organisms, in which one organism is benefited and the other organism is neither benefited nor harmed.
Amensalism is a type of interaction between two organisms, in which one gets harmed and the other is neither benefited nor harmed.