I would say, C. Because an controlled variable is an experimental element which is constant and unchanged throughout the course of the investigation.
Hierarchy - I don’t think I have the full context of the question but the word fits the best of its biology related
<h2>
"<em><u>
Earth or geoscience</u></em>
" investigates the interactions among the atmosphere, hydrosphere, biosphere, and geosphere.</h2>
Hmm i do not know but you can get dna from the cell.