How do lichens contribute to primary succession? lichens begin to break down rock to form soil. lichens decompose organic matter from animals and plants. lichens are nitrogen-fixing bacteria. lichens convert carbohydrates into fossil fuels.

The correct answer is- Lichens begin to break down rock to form soil.

Explanation:

Lichens are the symbiotic association of fungus and algae. Algae is the photosynthetic partner which provide food to the fungal partner and the fungus absorb nutrient for algal partner.

Lichens can be found in every region of the world and they also contribute to the primary succession. They colonize some bare rocks and degrade the rocks by secreting hydrolytic enzymes which starts the soil production process.  

As these lichens die they decompose to provide nutrients to the developing soil which allow other organism to colonize there. Therefore the right answer is- Lichens begin to break down rock to form soil.

equal distribution i think.