单项选择题 Weekly backups of the system are done on Sundays， and daily backups are done the rest of the week.  Which of following backup methods were used if the system crashes on Friday and only requires two backup sets to recover the system？（）

单项选择题 WhichofthefollowingistheMOSTlikelyconnectiontypeforabackupexternalmodem？（）

单项选择题 Anadministratorwantstolimithowmuchdataeachuserisstoring.WhichofthefollowingwillBEST addressthisissue？（）