간단한 영어 문법 문제 질문드려요

문법 문제 몇 가지 질문드려요.
1. Seen from a distance, the big tree looks like a giraffe.에서 Seen이 답인 것 같은데, 원래 문장은 As the big tree is seen from a distance, it looks like a giraffe.가 맞나요?
2. Having cut labor costs, the manufacturers reaped greater profits.에서 Having cut이 답인가요? 비용 절감이 먼저 일어난 일이라서 그런지 궁금해요.
3. Mother was vacuuming the floor in the living room, humming some popular tune.
4. He was thinking about what to do about the problem, tapping his fingers against his forehead.