You are using Oracle Database 10g. The LOG_ARCHIVE_FORMAT parameter is set to  ’LOG%t_%s_%r.dbf’.  Why is %r used in the file name format？（） 

Archive file format LOG_ARCHIVE_FORMAT is defined as arch_%s.arc. A week ago， you just archived arch_4.arch to tape， then removed all archived files to save disk space. Yesterday you saw arch_10.arc and arch_11.arc on the disk. Today， you see arch_3.arc in the archive directory.  Which two could you happened？（）