Which variable is changed by the scientists a controlled b independent c causation d dependent m pl

I’m stuck on this question cuz i’m stupid sksksksk

There are few cells in the body that do not undergo mitosis: most somatic cells divide regularly, some more than others. take for example the cells that line the digestive tract. these cells must be frequently replaced because they are constantly eroded by the movement of food through the tract. what mechanism(s) is/are in place to ensure that these cells are exact copies of the mother cell

Which methods are the most common for dealing with waste