Final answer:
Water is the substance that makes up the majority of every cell in the human body.
Step-by-step explanation:
The substance that makes up 75 to 90% of every cell in the human body is water. Water is vital for the functioning of cells and is involved in various biological processes such as transportation of nutrients, removal of waste, and maintaining cell structure. It acts as a solvent, allowing many important molecules to dissolve and participate in cellular reactions.
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