going in reverse....

hi,
DMV test is tomorow... I have some people saying that I must have both hands on the steering wheel at all times including when I am backing up and others that say that i can put my arm over the passenger's seat when backing up.
Putting my arm over feels a lot more natural and safe for me, but I was wondering if anyone knows if I am supposed to keep both hands on the wheel or not?
im in cali by the way,

ty in advanced for any help