Where would this phrase belong on the diagram? Studied animals In both X and Y In Z In X In Y

c- cold periods in earth's history during which glaciers covered much of the surface.

explanation:

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.