How many layers are there in iphone sdk?

(i).cocoa touch layer
(ii)Address book UI
(iii)UIKit
(iv)media layer
(v)audio toolbox
(vi)audio Unit
(vii)AV foundation
(viii)core Audio
(ix)core graphics
(x)media player
(xi)open GL ES
(xii)quartz Core
(xiii)core service layer
(xiv)address book
(xv)core foundation
(xvi)core location
(xvii)foundation
(xviii)system Configuration
(xix)core os layer
(xx)CF network
(xxi)security
(xxii)system
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