When we (to come) to the station, the train already (arrive). The pasSangers (to hurry) to occupy their seats in the

1. Идет речь о действии, завершенном к определенному моменту времени. Это Past Perfect.When we came to the station, the train had already  arrived.2. Идет речь о действии, длящемся какой-то период в прошлом. Это Past Continuous.The passengers  were hurrying to occupy their seats in the carriages.