6. When we ____ (arrive) at the station, the train ____ (leave).

Решение:

В данном предложении требуется два глагола в Past Perfect. Глагол 'arrive' в Past Perfect будет 'had arrived', а глагол 'leave' в Past Perfect будет 'had left'.

1. When we had arrived at the station, the train had left.

Ответ: had arrived, had left