Ответ:

  1. The sun was shining when we were on the beach.
  2. The pirates were sailing in shallow water when their ship hit the rocks.
  3. I was hiding the money when the police came.
  4. A lot of ships were attacking Blackbeard’s ship and Blackbeard was enjoying the action.
  5. The sun was going down and it was getting cold.
  6. It was getting warm, so we took off our coats.
  7. The pupils were putting the books in the cupboard when the teacher came in.
  8. Why was everybody laughing? Because Scott’s story was so funny.
  9. Some people were throwing a ball on the beach.
  10. Jenny was hurrying because she had lots of time.

Past continuous образуется с помощью was/were и формы глагола с окончанием -ing; он обозначает действие, происходившее в определённый момент в прошлом.