Why does a gain or loss develop when plant assets are retired?

Select answer from the options below

Assets must be depreciated; depreciation reflects asset cost allocation rather than value, and the gain or loss corrects net income over the life of the asset.

Retired assets must be sold or salvaged at disposition; sale or salvage amounts either above or below the book value of the asset result in a gain or loss.

Retired assets must cease operations at disposition; unscheduled stoppage $($as when a machine breaks$)$ results in a loss, while scheduled stoppage results in a gain.

Retired assets must undergo comparative valuation at disposition; fair value above book results in a gain, while fair value below book results in a loss.