1. What are their jobs? They're waiters. (singular) 2. What is this? It's an orange. (plural)
What is his job?
He is a waiter.
What are these?
They are oranges.
Just change the predicate, pronoun and noun. Come on!
This is a map. 2. That's an orange orange. 3. - what's this? - it's a watch
These are maps.
Those are orange oranges.
What are these?
They are watches.
This is an eraser plural
These are erasers