Answer: First, we will add the options below:
A. The textbook cost of first-year Drummand University students.
B. The year in school of Drummand University students.
C. The age of Drummand University students.
D. The cost of incidental expenses of Drummand University students.
The correct option is A. The textbook cost of first-year Drummand University students.
Explanation: The above research is focused on finding the cost of other expenses incurred in the process of getting a college education, apart from the tuition fee.
The researcher however, has chosen to focus the cost of incidentals like textbook costs for the research.
Since the researcher has chosen to use the cost of textbooks of 250 first year students, the variable of interest to the researcher is therefore the textbook cost of first-year Drummand University students.