Who are the students that are between 20 and 25 years of age? | Do you mean the last name or the first name of the students between 20 and 25 years of age? | What are the first names of the students who are between 20 and 25 years of age?
SELECT fname FROM student WHERE age BETWEEN 20 AND 25
students between 20 and 25 years of age refers to age BETWEEN 20 AND 25; first names of the students refers to SELECT fname;