Biology is the study of life, and uses the scientific method, the basis of science, to do so. Hypotheses are made, tested, and remade, until a theory is made, which then becomes Scientific law.
Only eukaryotes contain upper three but all cells contain "Contractile Vacuoles"
In short, Your Answer would be Option D
Hope this helps!
Because it serves as protection for a vital organ in the body. Also if the skull could move it would make the brain very vulnerable.
