The correct answer is C. They break down rock and form soil.
The lichens are an example which shows mutualism and they are found in every biome of the Earth.
The lichens have algae and fungus associated with them and they live in a mutualistic relationship with each other. Lichens can grow on soil where no other species can grow like rocks, barren soils and they enrich the soil on dying where other plants and trees can grow.
Lichens being pioneer species change the environment by building up the soil and liberating nutrients. Also the lichens contribute to the chemical weathering of the soil releasing phosphate along with erosion and weather conditions.
When the simple plants die, the wildflowers and other plants start growing replacing lichens or mosses.
From the given information it can be concluded that lichens alter the abiotic environment and favor other species of plants to grow by breaking down rocks from soil and providing nutrients.