单选题In user-managed backup and recover procedures， how are data files backed up？ （）A Using SQL commands.B Using SQL*Plus commands.C Using operating system commands.D Using Recover Manager commands.
题目
单选题
In user-managed backup and recover procedures， how are data files backed up？ （）
A
Using SQL commands.
B
Using SQL*Plus commands.
C
Using operating system commands.
D
Using Recover Manager commands.