Viruses can multiply very quickly, and so they can go through natural selection at a much quicker rate, allowing certain vaccine resistant mutations to take over a population.
<span>A: The proportions of a population that are at different age levels make up the population’s age structure. </span>
The first three are the same as those found in DNA, but in RNA thymine is replaced by uracil as the base complementary to adenine. This base is also a pyrimidine and is very similar to thymine. Uracil is energetically less expensive to produce than thymine, which may account for its use in RNA.
D... i took science last year
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