A—acceptance lettersB—adjustment lettersC—application lettersD—collection lettersE—complaint lettersF—credit lettersG—inquiry lettersH—memorandumsI—order lettersJ—reference lettersK—sales lettersL—news releasesM—annual reportsN—feasibility reportsO—investigative reportsP—progress reportsQ—trouble reportsR—trip reports ______调查报告 ______事故报告