We were friends.
- Were you (we) friends?
- Yes, we were. / No, we weren't.
- We weren't friends.
He became a pilot.
- Did he become a pilot?
- Yes, he did. / No, he didn't.
- He didn't become a pilot.
She washed her car yesterday.
- Did she wash her car yesterday?
- Yes, she did. / No, she didn't.
- She didn't wash her car yesterday.