This is the 9702nd most frequent Korean word.
고등학생이
"High school student."
In this sentence, '고등학생이' refers to the subject, specifying the group of people who need to study a lot.
고등학생이 공부를 많이 해야 합니다.
High school students have to study a lot.
Here, '고등학생이' identifies the subject who performed the action of leaving the school.
고등학생이 학교를 떠났습니다.
The high school student left the school.
In this case, '고등학생이' is used to describe a specific individual's characteristic, indicated by the demonstrative '그' (