What variable did the researchers intentionally vary in the experiment

Dependent Variable

Explanation:

There are two types of variable in any kind of experiment:

Independent Variable which are mostly known as inputs

Dependent Variables which are mostly known as outputs

In any experiment, the researches focus on observing the output values (dependent variables) by intentionally changing the inputs (Independent variables).

e.g. If we are observing the strain on any object, we try to change the value of stress on that particular object.

Here strain is a dependent variable whereas stress is an independent variable because it doesn't depend on whatever the value of strain may be.