Beijing to Lanzhou Flight Duration: How Far Is It?

This question should choose C. The question asks about the distance between Beijing and Lanzhou, using "flight" to indicate the mode of travel by plane. Option C's "2.5-hour flight" represents a flight duration of 2.5 hours. Options A and D's "2.5 hours' long" and "2.5-hour-long" represent time lengths, which do not fit the question. Option B's "2.5 hours flight" does not include a hyphen, violating English grammatical rules.