Answer:
Kidney
Explanation:
The kidney is the body system that regulates the acid base balance of the blood.
Multicellular organisms begin as a single cell. These cells then grow and undergo differentiation, the process by which cells develop specialized forms and functions.In multicellular organisms, cells are often organized into tissues, organs, and organ systems.
Answer: B. Water breaks down into oxygen molecules for respiration.
Water is the required for photosynthesis, a process by which plants (terrestrial and aquatic) makes their food by utilizing water as a reactant to produce oxygen and glucose as product. The glucose act as a source of energy for conducting various metabolic processes in plants but oxygen is released in the air.

This oxygen is necessary for terrestrial and aquatic animals for respiration. Therefore, water breaks down into oxygen by the process of photosynthesis, hence water plays important role in respiration in living beings.
I believe it’s A I think, I think I’m right
Is any member of a large class of gaseous, liquid, or solid chemical compounds<span>whose molecules contain carbon</span>