A secondary source is anything written after the fact
Animal phyla are primarily defined according to B. Patterns of embryologic development and adult body plans.
I think you're talking about histones. Histones are proteins found in eukayotic cell nuclei. Histones are what DNA wrap around so it fits inside the nucleus and helps with the formation of chromosomes.
Answer:
I'm more then sure it is A but let my know it im wrong if i am sorry :)
Explanation:
D. Number of protons in an atom's nucleus
