Beijing to Lanzhou Distance & Shanghai to Lanzhou Flight Duration Explained

The correct answer is C. 2.5-hour flight. \n\nThe phrase "2.5-hour flight" is the correct way to express the duration of the flight from Shanghai to Lanzhou. In English, when expressing the duration of an activity, we use the format of "number + unit + noun" (e.g. a three-hour movie, a two-day trip). Therefore, option C correctly follows this format by using "2.5-hour" to describe the duration of the flight and "flight" as the noun.\n\nOn the other hand, option A, "2.5 hours' long," is grammatically incorrect. In English, we do not use an apostrophe to indicate the possessive form of a noun before an adjective. Therefore, "2.5 hours' long" is not the correct way to express the duration of the flight.\n\nOption B, "2.5 hours flight," is also incorrect. In English, we use a hyphen between the number and the unit when expressing a compound adjective (e.g. a two-hour meeting). Therefore, "2.5 hours flight" is not grammatically correct.\n\nOption D, "2.5-hour-long," is redundant and unnecessary. The word "long" is already included in the phrase "2.5-hour," so adding another "-long" at the end is redundant. Therefore, option D is not the correct way to express the duration of the flight.