A part, or combination of parts, that performs a discrete and critical function in the operation of the unit of property is considered to be

A major component

An incidental material or supply

A substantial structural part

None of the above

AND

For depreciable property placed in service before December 30, 2003, a taxpayer may change the computation of depreciation to comply with the final MACRS regulations

Only by filing a Form 3115

By making an election and attaching a statement to its return

By filing amended returns beginning with the earliest year open under the statute of limitations

None of the above