The correct option is C
Step-by-step explanation:
Even though for all the incomes and the expenses we usually use the average rate for the year, however, in case of the allocations like the depreciation or an amortization of deferred revenue, we usually use the historical rate of when such allocation was made, that is when such an asset was purchased in the current case.
Therefore, the correct answer is "C" : The historical rate that was in effect when the related asset was purchased.