Which of the following is a nucleotide found in DNA? ​

I’m doing some practice exam questions for biology, and i’m not sure how to do these 3 parts to the question.

What are some characteristics of a free enterprise economy?

Study the picture of the ocean. which is the best example of an organism’s niche shown in the picture? a. the environment contains several of the same species of coral. b. the shallow area of the ocean meets the needs of the coral and the fish. c. the ocean has fish and coral that live in the same area. d. the coral take in food from the water and provide shelter for the fish.