IFRS permits companies to carry assets at historical cost or use a revaluation model for fixed assets. 

According to IAS 16, if revaluation is used:

1. 1. it must be applied to all assets in a class of assets.
2. 2. assets must be revalued on an annual basis.
3. 3. assets must be depreciated on the straight-line basis.
4. 4. salvage values must be zero.

 1 is correct.

 2 is correct.

 1 and 2 are correct.

 all of the choices are correct.