D) The AV valves are supported by chordae tendineae so that they do not blow back up into the atria during ventricular contraction.
The correct answer is "C".
Onion cell is a plant cell and human cheek cell is an animal cell. Hence, onion cell has a cell wall<span> but not in human cheek cells because animal cells do not have cell wall. Both cells have single nucleus. Since, human cheek cell is an animal cell, chloroplasts are cannot be seen in the human cheek cells.</span>
i believe the answer to be B
