Teacher:This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.
Teacher: Now, understand the problem? Solve this instance: Passage: Greece's rail network is estimated to be at 2,548 km. Rail transport in Greece is operated by TrainOSE, a subsidiary of the Hellenic Railways Organization (OSE). Most of the country's network is standard gauge (1,565 km), while the country also has 983 km of narrow gauge. A total of 764 km of rail are electrified. Greece has rail connections with Bulgaria, the Republic of Macedonia and Turkey. A total of three suburban railway systems (Proastiakos) are in operation (in Athens, Thessaloniki and Patras), while one metro system is operational in Athens with another under construction. Question: Who is TrainOSE a subsidiary of?
Student:
the Hellenic Railways Organization