Kate gathered three boxes of the same size made of different materials: glass, clear plastic, and aluminum painted black. she placed them on a window sill in the sun for an hour and then measured the warmth of the air in each box. in this experiment, the warmth of the air is a(n) independent variable dependent variable constant control

Dependent variable.

Explanation:

Based on the description, the experiment is designed to confirm or reject a hypothesis about a heat absorption patterns by  hollow objects with different transparency. Temperature appears to be the main target variable of interest - this is the dependent variable. Material that each box is made of (specifically, its transparency) is in this case the independent variable, which is determined by the experimenter.