The correct answer is: C. asset identification number
A file key is a unique identifier for a record in a file. It is used to locate the record in the file and to link the record to other files. The asset identification number is a unique identifier for an asset. It is used to track the asset throughout its life cycle, from acquisition to disposal.
The fixed asset account number is the account number used to track the asset in the general ledger. The acquisition date is the date on which the asset was acquired. The depreciation account number is the account number used to track the depreciation of the asset.
None of the above options are the file key of the fixed assets file.