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Consider a database with the following three relations:

- CREDITS (STUDENT; COURSE)
- OFFERS (TEACHER; COURSE)
- BELONGS (TEACHER; DEPARTMENT)

Given below is a code in query language QUEL. Describe in one English sentence the query posed by the given QUEL program.

range of s is CREDITS range of t is OFFERS retrieve into LIST 1 (1=s. STUDENT) where s.COURSE=t.COURSE and t.TEACHER="Dr.X" retrieve into LIST 2 (1=s.STUDENT) where s.COURSE =t.COURSE and t.TEACHER ="Dr.Y" retrieve into LIST3 (1=STUDENT) where s.course =t.COURSE and t.TEACHER ="Dr.Z" range to e1 is LIST1 range of e2 is LIST2 range of e3 is LIST3 retrieve(E1.I) where e1.I=e2.I and where e1.I=e3.I