The action or fact of forming a united state that seems as the best answer
The answer is B) Genetic variation
The difference between extrusive and intrusive rocks are how they cool
down. Extrusive rocks cool down quickly and are created by lava; because
of this they have very small, fine-grained crystals. Intrusive rocks
cool slowly beneath the surface of the earth and are created by magma;
because the cooling process is very slow the rocks have very large
crystals.
I think it's D) atmospheric carbon dioxide.
DNA replication occurs due to an enzyme. The DNA unzips, and the enzyme pieces together new parts to make each half its own full DNA strand.