The part of the stem that gives rise to this pattern is : B. xylem
xylem is responsible in transporting water and nutrients. It die after a year or so and will leave the concentric pattern as it die
hope this helps
If I am not wrong, I believe the answer is Producers. The reason as to why I say that producers is the answer is because in every food chain, there needs to be a base. That base is what provides the starting energy that will later on move up in the food chain.
It is important to look at birth and death rates while considering population size because they determine the population size
those are nucleotides
since all three of them contain deoxyribose (because there's only one hydroxil group) they are DNA nucleotides
the first nucleotide has cytosine as it's nitrogenous base
the second nucleotide has adenine as it's nitrogenous base
the third nucleotide has thymine as it's nitrogenous base