C. When there is an equal number of molecules on each side
Explanation:
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The pit that marks the location of the umbilical cord after birth is known as the navel or belly button. All animals that grow placenta during fetal development will have a navel or belly button. The scientific name of the structure is the umbillicus. It can be a depression in some individuals or raised in others.
I believe vestigial structures are evidence of evolution because organisms inherit anatomy from their ancestors.
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