I NEED HELP FOR THIS QUESTION IT'S ONLY ONE. I WILL GIVE BRAINLIEST TO THE ONE WHO ANSWERS FIRST The Gastropod is found in multiple rock layers. What does this indicate?

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Agene pool: a) is the collection of all the alleles found in a single species b) is the collection of all the alleles found in a single population c) is the collection of all the chromosomes found in a single population d) is the collection of genes in a species that allow the individuals to swim