Past perfect + Past Simple
Incorrect : The train left before I reached the Station.
Correct : The train had left before I reached the station.
Note: When we refer to two consecutive past actions in the same sentence using the conjunction ‘before’ or ‘after’, the action which was completed first is put in the past perfect tense and the second action is put in the past indefinite tense.
Incorrect : I reached the station after the train left.
Correct : I reached the station after the train had left.-