National Research Council (U.S.). Transportation Research Board. Committee A3B05. (1990). Travelers' services: Research problem statements. Transportation Research Board, National Research Council.
शिकागो शैली (17वां संस्करण) प्रशस्ति पत्रNational Research Council (U.S.). Transportation Research Board. Committee A3B05. Travelers' Services: Research Problem Statements. Washington, DC: Transportation Research Board, National Research Council, 1990.
एमएलए (9वां संस्करण) प्रशस्ति पत्रNational Research Council (U.S.). Transportation Research Board. Committee A3B05. Travelers' Services: Research Problem Statements. Transportation Research Board, National Research Council, 1990.
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