Answer:
a. the amount of stress
Step-by-step explanation:
Variable: In psychological research or experiment, the term variable is defined as something that can either be varied or changed, for example, a value or characteristics. A variable is being used in an experiment to determine to see the effect of the change to one thing will cause the change in the other thing or not.
Types of variables:
1. Independent variables: controlled or manipulated.
2. Dependent variables: gets affected by the independent variable.
3. Control variables: constant.
In the question above, the variable is the amount of stress.