Depreciation

I have a problem with this question:
Which of the following statements are correct?
a. all non-current assets must be depreciated
b. straight line depreciation is usually the most appropriate method of depreciation
c. a change in the chosen depreciation method is accounted for retrospectively, with all previous depreciation charges reversed and recalculated
d. depreciation charged must be based on the carrying amount of an asset (less residual value if appropriate)

option D is given as a correct answer. I think It is correct if reducing balance method is used, but if we use straight line method, depreciation charge should be based on original cost less residual value, am I wrong?