Answer:
(C) Whether or not a subject attends preschool
Step-by-step explanation:
In research studies, variables are used to explain differences in another variable. The explanatory variable (also known as independent or predictor variable) is used to explain differences in the response variable (dependent or outcome variable).
It is important to know that the explanatory variable is the variable that is manipulated by the researcher.
The facts that are not being manipulated are the income of the children studied, and what happens after attending or not preschool program. The variable the researcher is manipulating is the assignation to groups that will or will not attend preschool. Therefore the correct answer is:
(C) Whether or not a subject attends preschool
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