Answer:
Entire students with valid email ID on records
Explanation:
In a data set, population refers to all entities or members that can be part of the study. Sample refers to the selected group from the population that actually form the part of study.
Population includes everyone who can be included in the study. In this case, the study is focused on estimating number of students at the university who spend on books each term. Here, entire student body with valid email id forms the population for the study. Valid email Id is necessary as the method used to take survey is through emails.
