Which is not a reason that Internet Service Providers prefer to use PPP over Ethernet (PPoE)?（） ["access control and billing can be done on a per-user, rather than a per-site basis","supports Link Fragmentation and Interleaving ","provides the ability to connect a network of hosts over a simple bridging access device","provides a consistent means of authenticating users (RADIUS for example)"]
在动态建模机制中，一消息来完成对象之间的交互，用（）来描述系统的行为。 ["状态图和顺序图","协作图和活动图","数据流图和实体关系图","对象图和包图"]
Your Certkiller .com database is in ARCHIVELOG mode. The data file that belongs to the SYSTEMtablespacehas become corrupted. Up to what point can you recover the database？（） ["Until last commit","Until the time you perform recovery","Until the time the date file got corrupted","Until the point where the last transaction begun","You cannot recover the SYSTEMtablespaceand must re-create the database."]
You work as a database administrator for Certkiller .com. The UNDO_RETENTION parameter in your database is set to 1000 and undoretention is not guaranteed. Which statement regarding retention of undo data is correct？（） ["Undo data becomes obsolete after 1，000 seconds.","Undo data gets refreshed after 1，000 seconds.","Undo data will be stored permanently after 1，000 seconds.","Committed undo data would be retained for 1，000 seconds if free undo space is available.","Undo data will be retained in the UNDOtablespacefor 1，000 seconds， then it gets movedmovedto the TEMPORARYtablespaceto provide read consistency."]
苏州港太仓港区六期围滩吹填工程的防台防汛工作尤为重要，因此（）安全应急预案是应急预案中的重要部分 ["岸上","水上","室内","陆地"]
简述使用Command进行数据更新的步骤。
