Active: Unknown factors delayed the 9:15 train from Pittsburgh.
Passive: The 9:15 train from Pittsburg was delayed by unknown factors.
Explanation:
The sentence is already active. The object of the sentence is ‘the train from Pittsburgh’ and the subject is ‘unknown factors’. The subject of the sentence performs an direct action over the object (delayed), so it is an active sentence. When we give more importance to the object of the sentence it becomes passive, as it is stated in the second sentence: The 9:15 train from Pittsburg was delayed by unknown factors.
