The narrator tells us that her father describes what happened to the mary celeste in what way? as a "lost cause" – a sad occurrence from the past
as a "cold case" – an investigation that cannot be completed
as an "open file" – a mystery still waiting to be solved
as a "dead end" – an event no one can fully understand

As an "open file" – a mystery still waiting to be solved.

Explanation:

In this story, we learn that the "Mary Celeste" is considered an "open file" by the father, as it is a mystery that is waiting to be solved. The Mary Celeste was a ship that was found 400 miles east of the Azores on December 5, 1872. It was found by the crew members of the British brig Dei Gratia. The Mary Celeste had left New York City eight days earlier and should have safely arrived in Genoa, Italy. However, the ship was discovered to be empty, with no sign of damage. No one knows what happened to the crew, which makes this a mystery still waiting to be solved.

thousands of people

explanation: