Final answer:
The amount of sleep that laboratory rats received in the study is an experimental variable, as it is the controlled input changed by the researcher to observe its effects on the eating patterns. The correct option is D.
Step-by-step explanation:
In the context of a weekly study observing the eating patterns of laboratory rats while manipulating their sleep, the amount of sleep received would be considered the experimental variable. This variable is the controlled input of the experiment, which in this case, the researcher is changing to observe how it affects the rats' eating patterns. Therefore, the correct choice is d) variable.
A variable in an experiment is something that the researcher can change or control in order to study its effects on other variables, often referred to as the dependent variables.
For instance, in the provided example of the psychologist interested in the effect of tableware size on food consumption, the size of the tableware is the experimental or independent variable (explanatory variable), and the amount of food consumed is the response variable, which depends on the manipulation of the independent variable.