I'm not sure what the lesson is, but the answer that makes sense the most is number. Number because most lessons in subject-verb agreement concerns the singularity and plurality of the subject at hand
It is correct but you could use words that people would more understand.
If you were referring to groceries or things you buy from the store, you could say:
He left all his items on the bus.
He left all his groceries on the bus.
(<em>Your answer is great this is just a suggestion) </em>
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.
What word is underlined on your assignment?