두 문장을 한 문장으로 합치는 방법 질문드려요

두 문장을 한 문장으로 합치는 문제인데요.
“The soldier was wounded in a war. He was sent to a military hospital.”의 답은 “The soldier wounded in a war was sent to a military hospital.”라고 생각했는데, 맞는지 궁금합니다.
“The tree house was built in my backyard. It attracted a number of tourists.”도 “The tree house built in my backyard attracted a number of tourists.”라고 생각했어요.
앞의 두 문제에서 어떤 문장이 맞는지 이유도 설명 부탁드려요.
세 번째 문장은 “The picture painted by this young artist was auctioned off at a high price.”가 답이라고 합니다.