火灾事故广播设备的检验，应按实际安装数量的（）%～（）%进行下列功能检验：一、在消防控制室（）广播；二、共用的扬声器强行（）试验；三、备用扩音机控制（）试验。上述控制功能应正常，语音应清楚。
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You have been recently hired as a database administrator. Your senior manager asks you to study the production database server and submit a report on the settings done by the previous DBA. While observing the server settings， you find that the following parameter has been set in the parameter file of the database： REMOTE_OS_AUTHENT = TRUE What could have been the reason to set this parameter as TRUE？（）
A. to enable operating system authentication for a remote client
B. to restrict the scope of administration to identical operating systems
C. to allow the start up and shut down of the database from a remote client
D. to enable the administration of the operating system from a remote client
E. to disable the administration of the operating system from a remote client
Which two statements about subqueries are true? （）
A subquery should retrieve only one row.
B. A subquery can retrieve zero or more rows.
C. A subquery can be used only in SQL query statements.
D. Subqueries CANNOT be nested by more than two levels.
E. A subquery CANNOT be used in an SQL query statement that uses group functions.
F. When a subquery is used with an inequality comparison operator in the outer SQL statement, the column list in the SELECT clause of the subquery should contain only one column.
DF4B型内燃机车冷却器共有（）冷却单节。
A. 58个
B. 60个
C. 56个
D. 52个
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