The Average Number of Units Earned Per Semester by College

The average number of units earned per semester by college students is suspected to be rising. A researcher at Calendula College wishes to estimate the number of units earned by students during the spring semester at Calendula. To do so, he randomly selects 100 student transcripts and records the number of units each student earned in the spring term. Identify the variable of interest to the researcher.

A) the number of students enrolled at Calendula College during the spring term
B) the average indebtedness of Calendula College students enrolled in the spring
C) the age of Calendula College students enrolled in the spring
D) the number of units earned by Calendula College students during the spring term