Which of the six classes of nutrients is foremost in quantity and must constantly be replaced? a. Protein
b. Water
c. Vitamins
d. Fat

Water.

Explanation:

Water makes up 60% of a human body, and can be loss due to peeing, sweating, etc. In fact, the human generally loses so much water that the average human is suggested to drink 15 cups of water a day, depending of course on job, amount of exercise, body build, etc.

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im 100% sure its all of the above.