Answer:
That statement is true
Explanation:
In research, generalization occurs when we make a statement that applicable to a certain group or sitaution.
In the example above, Sandra wants to study study how students in their senior year of high school prepare for college. This means that the group that she wants to generalize are the students in the senior year of their high school.
If Sandra only visit the elite boarding school and use it as her only subject, the result wouldn't represent the students in senior high school as a whole. The students in elite high school are more likely to be well-off and have better learning system compared to the students in average high school.
This is why Sandra needs to visit more schools with different criteria in order to make general claims about the seniors.