There are 25 elements found in living things. How many of these elements are found in some organisms but not all?

Six elements—carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur—are found in all living organisms. Subtract those 6 from the 25 elements found in living things: 25 − 6 = 19. So 19 elements are found in some organisms but not all; the correct choice is 19.

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