Beijing to Lanzhou Distance & Correct Time Expression in English

This question chooses C. ABD is incorrect because in English, a phrase indicating the length of time is usually composed of a number + unit (e.g., hour) + adjective (e.g., long). 2.5-hour-flight is incorrect because in English, time after the decimal point is usually not connected with a hyphen, but is expressed using a decimal point. Therefore, the correct expression is 2.5-hour flight.