Sarah wants to know which brand of nail polish lasts the longest without chipping. she buys 4 types of nail polish - essie (which she normally uses,) butter, opi, and sally hanse. every sunday for 4 weeks she paints her nails with a different brand of nail polish and records how many days she lasts before she gets her first chip. she makes sure to use the same bottom coat and top coat with each types of nail polish, and she makes sure to do the same weekly routine each week so that her nails aren't getting treated more roughly
different weeks.

The answer is explained below.

Explanation:

Independent variable is the one that is changed and controlled: the nail polish Sarah uses.

Dependent variable is the one that is studied, the result of the dependent variable: how long the nail polish lasts.

Hypothesis is the statement that has to be proved or declined during the experiment: different nail polish lasts a different period of time without chipping.

The control group is the not exposed to changes and the independent variable is part of this group: when Sarah paints her nails (4 Sundays in a row) and the type of bottom coat and top coat as well as the weekly routine.

The experimental group contains the independent variable and it is changed for the group: the type of nail polish.

The constants are Sally since she performs the experiment; the period of research, the routine and the coats.

c is the correct answer!