They were at work at that time.（改为否定句和一般疑问句并作肯否定回答）

They weren't at work at that time.
Were they at work at that time?
Yes,they were.
No,they weren'tIt was hot yesterday..（改为否定句和一般疑问句并作肯否定回答）It wasn't hot yesterday.Was it hot yesterday?Yes,it was.No, it wasn't