填空题

[听力原文]11-15
We left London on June 21st and flew to Athens on a British Airways flight. We left London at about 11:00 in the morning and arrived in Athens at about 3:00 in the afternoon. It was raining in London when we left, but it was fine and warm in Athens. After we came out of the airport building, we took a taxi to the town center. We stayed for three nights at a hotel. While we were in Athens we visited some of the sights and we went to a concert.
On our fourth day we went to Athens Airport early in the morning and took an Olympic flight to a beautiful Greek island, Santorini. We stayed at a small hotel in the capital of the island. The hotel was very high and we had a wonderful view of the sea and the island. We enjoyed the typical Greek food in the hotel’s restaurant and we enjoyed walking down the beaches, too.
After we had spent a week on this island, we flew back to Athens for another three nights. We visited a fishing village on a small island near Athens. We also went to a bar in the city where we met many local Greeks. We talked to them and had a nice evening with them.
Then we flew back to London on an Athens Airways flight. It was a wonderful holiday and we enjoyed ourselves very much.

What flight did they take
They took a（）flight.