What's he doing at the post office?
He's mailing.
What's he doing at the park?
He's kicking.
What are they doing at the library?
They're borrowing.
What's he doing at the department store?
He's shopping.
What's he doing at the movie theater?
He's watching.
What's she doing at the library?
She's borrowing.
What are they doing at the movie theater?
They're watching.
What's she doing at the grocery store?
She's buying.