Directions: The following is a list of terms related to Security. After reading it, you are required to find the items equivalent to (与…等同) those given in Chinese in the table below. Then you should put the corresponding letters in the brackets on the Answer Sheet, numbered 51 through 55. A ----------------- air traffic control system B ----------------- armed police C ----------------- crime prevention D ----------------- entry requirement E ----------------- international criminal police organization F ----------------- level of security G ----------------- picket line H ----------------- police station I ----------------- patrolling vehicle J ----------------- safety precaution measure K ----------------- safety control device L ----------------- security command center M ----------------- security service N ----------------- security control center O ----------------- security personnel P ----------------- valid documents Q ----------------- security monitoring and control Examples: ( M ) 保安服务 ( G ) 警戒线 51. ( ) 空中交通管制系统 ( ) 安全预防措施 52. ( ) 巡逻车 ( ) 武装警察 53. ( ) 国际刑警组织 ( ) 有效证件 54. ( ) 入境要求 ( ) 安保人员 55. ( ) 安全保障级别 ( ) 安全监控