A third person narrator knows all the characters' feelings and thoughts, an author might choose this perspective to let the reader know everything the characters are feeling and what's going on. This gives a broader perspective on the story and can influence the readers opnion.
Answer:
1. We have lost the sculpture
= Sculpture was lost by Us.
2. They saw him crossing the road.
= The road was crossed by them.
3 .We can do this work within a week.
= The Work could be done within a week.
