A young girl whips her hair over her head in a public pool
A girl is in a public pool.
A boy is in a pool.
A good case study has selected appropriate interviewees, so no justification is needed.
I don't have a clear memory about the details of my life  when I was ten.
It was a sad story.
A person is driving home.
A British cannonball made a crack in the throne in 1857.
This information is always easy to access.