박상완이

In a sentence

• 박상완이는 학교에서 공부를 매우 열심히 합니다.

  Park Sangwan studies very diligently at school.

  In this sentence, '박상완이' is the subject of the sentence, using the subject particle '이' to indicate the topic of the clause.

• 이 책은 박상완이가 지난주에 읽은 책이에요.

  This book is the one Park Sangwan read last week.

  Here, '박상완이가' includes the subject particle '가' to indicate that Park Sangwan is the one who performed the action of reading.

• 어제 저는 박상완이를 공원에서 만났습니다.

  Yesterday, I met Park Sangwan in the park.

  In this example, '박상완이를' utilizes the object particle '을' (with the associated form when ending in a vowel) to mark '박상완' as the object of the verb '만나다' (to meet).