Although Lichens Look Like Single Organisms, They Are Actually an Association

Although lichens look like single organisms, they are actually an association between a fungus and a photosynthetic partner, usually an alga.The lichen association is considered mutualistic, but the relationship also shows some features of parasitism.Which fact about lichens suggests parasitism rather than mutualism?

A) One kind of fungus can partner with more than one kind of alga.
B) The fungal species that occur in lichens almost never occur outside of lichens.
C) Nutrients always flow from algae to fungi but do not always flow from fungi to algae.
D) Some lichens live in habitats where no fungi or algae can survive except within lichens.
E) Lichens most often reproduce asexually with small clusters of cells from both partners.