Which of the following best explains why fossil evidence from each era has different organisms? Organisms adapted to the new environment rapidly by the end of each era creating new species.

Organisms evolved before the end of each eon creating new species.

Major mass extinctions of organisms occurred at the end of each era allowing new species to evolve.

Major mass extinctions of organisms occurred in the middle of each era allowing new species to evolve.

During crossing-over, a. genetic material is exchanged between nonsister chromatids, resulting in new combinations of alleles. b. nonsister chromatids from each homologous chromosome of a tetrad are exchanged, resulting in new combinations of alleles. c. one homologous chromosome of a tetrad is exchanged with another tetrad, resulting in new combinations of alleles. d. sister chromatids from each homologous chromosome of a tetrad are exchanged, resulting in new combinations of alleles. e. genetic material is exchanged between sister chromatids, resulting in new combinations of alleles.