토익문제중에 구조가 안뚤려서 질문을올려봅니다

Since the donation contained perishable food items, volunteers were concered it might already have expired when it reached its final destination

이란문장에서 it might already have expired 가 주절인가요? 아니면 volunteers were concered 가주절인가요? 만약 volunteers were concered 가 주절이면 it might~절의 정체가궁금하고 반대로 it might~절이 주절이면 volunteers were concered 란절의 정체가궁금하네요 concered 가 5형식으로 쓰여서 목보로 it might~의절을 받은건가요 ??