D is the answer your looking for
I’m in chemistry too. Giving this my best guess I’d say
Independent: Gem Mines
Dependent: Gem clarity
Controlled: Temperature
Each element<span> can usually be classified as a metal or a non-metal based on their ... They are usually </span>dull<span>and therefore show no metallic </span>luster<span> and they do not reflect ... </span>Dull<span>, Brittle solids; Little or no metallic </span>luster<span>; </span>High<span> ionization energies; </span>High<span> ...</span>