4 A student conducts an experiment at home to test the effect of different covers on the melting rate of ice. The student places identical ice cubes on separate trays of known
mass. The student covers each tray as shown below. The trays are placed on the same
table. After ten minutes, the student removes the covers, discards the excess water,
and calculates the mass of each ice cube. Which of these is a constant variable (or
controlled variable) in the experiment?
initial mass of each ice cube
final mass of each ice cube
the uncovered ice cube
material covering the ice cubes