Answer:
I think the answer is B, Rivers. Mountain ranges don't really help the environment much as can mostly only change the climate.
DNA structure. DNA is made up of molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C).
<span>What MUST occur before mitosis and meiosis can occur is B) DNA replication. DNA replication is a process of copying DNA into an identical copy. Before mitosis, the genetic material of the mother cell must duplicate so that each daughter cell have the same amount as the mother cell. On the other hand, meiosis is a reductive division. But meiosis II is similar to mitosis, so DNA replication is also necessary.</span>
