用户帐户被锁定，是因为（）。 ["帐户长时间没有被使用","帐户超过了帐户锁定阈值","系统管理员禁止该用户帐户","帐户超过使用期限"]
If the temperature in the icebox is too high, the trouble could be（） ["a clogged scale trap","air in the system","automatic controls not functioning properly","insufficient cooling water to the condenser"]
区域经济政策指政府（）的旨在协调、促进区域经济发展的各种法令、条例和措施。 ["管理","制定","实施"]
Air or noncondensable gas is removed from a refrigeration system by a （） ["separating chamber","system of baffles","purge valve","vacuum reducing valve"]
在TCP/TP协议中，进行路由选择的层次是（）。 ["网络层","数据链路层","传输层","应用层"]
何谓高频闭锁距离保护？高频闭锁距离保护有何优缺点？
