"Natural selection<span> is the differential survival and reproduction of individuals due to differences in </span>phenotype<span>. It is a key mechanism of </span>evolution<span>, it is a change of </span>heritable traits<span> in a </span>population<span> over time"</span>
RNA stands for ribonucleic acid. It's primary function is to make ribosomes, hence the answer is 'a'
Most things can't be explained or it hasn't been discovered yet. Science is all about asking questions and figuring out how things are the way they are.