Its most definitely A, hope this helps :)
Answer:
A nucleotide is the basic building block of nucleic acids. RNA and DNA are polymers made of long chains of nucleotides. A nucleotide consists of a sugar molecule (either ribose in RNA or deoxyribose in DNA) attached to a phosphate group and a nitrogen-containing base.
Answer:
Gas exchange takes place in the millions of alveoli in the lungs and the capillaries that envelop them.
Explanation:The body's circulation is an essential link between the atmosphere, which contains oxygen, and the cells of the body, which consume oxygen.
C:when a person is choking
