Final answer:
The variable that uses 0 to represent 'single' and 1 for 'married' is a categorical variable because those numbers serve as labels for categories rather than quantities.
Step-by-step explanation:
The variable in question, which takes on values of 0 and 1 to indicate an individual's marital status-being single or married, respectively-is a categorical variable.
This is because the numbers are used as labels to denote membership in a category, rather than numerical values representing measurable quantities. Indeed, in this context, the numerical aspect of data is not relevant-it doesn't make sense, for example, to find an average between 'single' and 'married'.
The correct response to the student’s question is d. Categorical because a categorical variable consists of names or labels of groups of individuals.