听力原文：An airline is an organization which provides aviation services for passengers and

听力原文： An airline is an organization which provides aviation services for passengers and cargo. It owns or leases airlines for reasons of mutual benefits. The scale and scope of airline companies range from those with a single airplane carrying mail or cargo, to full service international airlines operating many hundreds of airplanes of various types. Airline services can be categorized as intercontinental, intra-continental, regional or domestic and may be operated as scheduled service or charters. These variations in the types of airline companies, their operating scope, and the routes they serve, make analysis of the airline industry complex. But one thing is certain: The industry is heavily influenced by the market now. In the past 50 years or so, the general trend of ownership bas gone from government-owned or government-supported to independent, for profit companies. This is a result of the government permitting greater freedom. This trend is not yet consistent across all airlines in all regions. The demand for air travel services depends on other things: needs for cargo transportation, business passenger demand, leisure passenger demand, which are all influenced by macroeconomic activity in the market. These trends are highly seasonal, and often depend on day-of-week, or time-of-day. The industry is cyclical. Four or five years of poor performance are followed by five or six years of gradual improvement in performance.

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A．The market plays an important role in airline service.

B．It introduces the history of the aviation service.

C．It describes airline companies.

D．It introduces the scale and scope of airline companies.