구조 질문드려여

In no place , save from the windows in the walls , was there an available exit.

 전치사 save가 그 뒤에서 또 전치사+ 명사 구조를

받았는데 전치사가 이렇게 전치사구를 목적어로

가질수 있어요?ㅠ.ㅠ

In Africa , there is a unique kind of woodpecker. when it is ready to mate , it locates a proper tree with a hole sufficient for the female and male to enlarge for their nest. female begins to carry mud from the creek bank back to the nest to close in the opening of the nest. over several days , she will work until there is only a tiny slit in the mud-filled opening large enough to insert her bill.

back은 동사인가요 전치사인가요?ㅠ.ㅠ

large enough to~ 는 slit을 꾸미는 후치수식 맞나용?~?