What is any part of an experiment that can change? A) control B) experiment C) variable D) factor

Defidently don't start answering as quick as possible some teachers do say to read the hardest first but i would think the most logical answer is c carefully read the passages and i structions

    the box has volume x^2h.  the cylinder has volume x^2h/4.  v = πr^2h = x^2h/4  πr^2 = x^2/4  r^2 = x^2/(4π)  r = x/(2√π)  b

Maybe c. im not too positive