多项选择题 Youareinthemiddleofatransactionandverycrucialdatahasbeenmodified.Becauseofahardwarefailure，theinstancehasshutdownbeforesynchronizingallthedatabasefiles.Whichtwostatementsaretrue？（）

单项选择题 Oneoftheusersessionswasterminatedabnormallyinthemiddleofatransaction.WhatdoesOracledatabasedotorecoverit？（）

单项选择题 Initially， for the Automatic Workload Repository （AWR） statistics， the retention period is set to 7 days， the collection interval is set to 30 minutes and the collection level is set to Typical in your production database.  You have been using the Memory Advisor for the last three months to generate recommendations for tuning memory components. However， when you observe the Memory Advisor on a Friday， you find that the statistics are available only for two days， Thursday and Friday， of that week.  What would have caused the statistics to be removed？（）