Your friend tells you that some of the carbon atoms in his body were previously part of another living organism. This is

A) possible only if he is a cannibal.
B) possible since carbon cycles through the ecosystem.
C) impossible since carbon can't enter a living system more than once.
D) highly unlikely since carbon does not cycle like other elements.
E) unlikely because we don't have any carbon atoms in our bodies.

Carbon cycles through the ecosystem, meaning that it can be taken up and used by living organisms multiple times. Therefore, it is possible for some of the carbon atoms in your friend's body to have previously been part of another living organism. Option A is incorrect because being a cannibal is not necessary for carbon to cycle through the ecosystem. Option C is incorrect because carbon can enter a living system multiple times. Option D is incorrect as carbon does cycle like other elements. Option E is incorrect because we do have carbon atoms in our bodies.