which RAID implementation?

Mirroring is another name for which RAID implementation?

A.
RAID level 2

B.
RAID level 3

C.
RAID level 5

D.
RAID level 1

Explanation:
RAID level 1 mirrors data from one or more disks to another disk or
set of disks. Each drive is normally mirrored to an equal drive that is updated at
the same time, thus allowing for recovery from the other drive if one drive should
fail.