Fungi form lichens by living in a close relationship with an algae. The fungus provides a
protective home for the algae, and gathers mineral
nutrients from rainwater and from dissolving the
rock underneath. The algae gathers energy from
the sun using photosynthesis. Both organisms
share their nutrients with each other.
A. Commensalism
B. Parasitism
C. Mutualism
D. Competition

Commensalism

Explanation: Well you can already eliminate parasitism because that is when an organism leeches off another. Mutualism is when one organism needs to depend on another compared to A where both are benefited.  Then you can eliminate d because competition is when two organism compete with each other for survival not benefiting them both.

dna is made up of six smaller molecules -- a five carbon sugar called deoxyribose, a phosphate molecule and four different nitrogenous bases (adenine, thymine, cytosine and guanine).

chert is a sedimentary rock composed of microcrystalline or cryptocrystalline silica. with this little bit of information, you can come to the conclusion that your answer is c.  

explanation: