The correct answer to this open question is the following.
These are the correct form of verbs.
5.- When his friends saw the Picasso, they were amazed.
6.- When his friends saw the Picasso, they left the office.
7.- He put his elbow through the canvas.
8.- La Réve put into a vault to keep it safe.
These are the correct form of the verbs for the sentences.
It is important to write the correct form of verbs so the sentences have the proper meaning and can be understood. Grammatics is very important in academic writing.