I dont think i'm answering your question, but the sun turns into a red giant, and the more it gets bigger it gets, the more closer it is to the planets. Then eats up the the planets later on, and explodes. Dont know if im correct tho sorry
Decaying uranium atoms in the earth's crust result in Radon gas. Radon gas cannot be synthetically or commercially produced. It is produced as the result of the natural breakdown of uranium i.e. decaying uranium atoms. Radon gas is a naturally occurring radioactive gas. People are exposed to Radon gas via the inhalation and ingestion of the gas. Because it is found in the ground, water or building materials, Radon gas can enter work buildings as well as private dwellings.
Algae will be overgrown and larger fish will begin to die out as the carrying capacity has lowered due to a limit in food.
C is the most likely answer to this question.