I. A—air traffic control system J—safety precaution measure B—armed police K—safety control device C—crime prevention L—security command center D—entry requirement M—security service E—international criminal police organization N—security control center F—level of security O—security personnel G picket line P—valid documents H—police station Q—security monitoring and control I—patrolling vehicle ( ) 安全保障级别 ( ) 安全监控