液压破拆工具的快速插头，连接和分离必须在什么情况下进行？（）
A. 发动机关机的情况下
B. 油管内无油压的情况下
C. 安全情况下
D. 无火花
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直剪试验分为快剪、固结快剪和慢剪试验，下列（）可以进行快剪试验：
A. 粘土；
B. 砂土；
C. 粉土。
Which two statements are true about broadband cable （HFC） systems？（）
A. Cable modems only operate at Layer 1 of the OSI model.
B. Cable modems operate at Layers 1 and 2 of the OSI model.
Cable modems operate at Layers 1， 2， and 3 of the OSI model.
D. A function of the cable modem termination system （CMTS） is to convert the modulated signal from the cable modem into a digital signal.
E. A function of the cable modem termination system is to convert the digital data stream from the end user host into a modulated RF signal for transmission onto the cable system.
In order to avoid misconnections due to a failed node in a Bidirectional Line Switched Ring (BLSR), Alarm Indication Signals (AISs) are sent on every channel normally terminating in that node. What is the name of this process?（）
A. trunking
B. squelching
C. nodal bypass
D. bridge and roll
E. node failure insertio
数据库管理系统DBMS提供的功能包括四个方面，分别是（）、（）、（）、（）。
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