问题：

[单选]

You executed the following command in Recovery Manager （RMAN）：  
RMAN> REPORT NEED BACKUP days 3；  
What is the output of this command？（）  

A .  a list of files that require a backup within three days
B .  a list of files requiring more than 3 days of archive logs to apply
C .  a list of files that RMAN recommends be backed up only once in every three days，based on low volatility
D .  a list of files for which a backup has already been performed in the last three days and which is required to be backed up again based on the high number of transactions performed on them