Declining balance applies a rate to carrying amount, so salvage bounds the total rather than entering each year's arithmetic.
Declining balance applies its rate to carrying amount, not to the depreciable amount.
The activity method estimates life in units of output rather than in years. It is still an estimate of how long the asset will serve.
Total depreciation is the same under every method. Only its timing differs, which is the point a reviewer holds onto.
Answer: a
Choice a. The inputs are shared; declining balance is the one that leaves salvage out of the annual calculation and uses it as a floor.