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What is the most likely reason that horses and mountain goats have hooves?
They have homologous structures because they have a common ancestor
They have analogous structures because they have a common ancestor.
These are vestigial structures in both animals because they are not used.
These are similar structures due genetic mutations.

They have homologous structures because they have a common ancestor

Explanation:

vestigial structures can be considered evidence for evolution, the process by which beneficial heritable traits arise in populations over an extended period of time.

the real answer is b. scintillation counter

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.