Will give brainliest answer
both primary and secondary succession begin with pioneer species that?
a. change the area and make it safer from predatory organisms
b. invade the area so that new organisms cannot be established.
c. modify the area and allow larger and more complex organisms to appear
d. use up all the existing resources and prevent establishment of non-native organisms

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.