Answer:
c. useful life.
Step-by-step explanation:
In the case of the patent, the cost price of the patent could be amortized over its useful life but that should not be more than its legal life. The legal life is 20 years
Therefore as per the given situation, the option c is correct as the cost of the patent could be amortized by the company over its useful life
Therefore the same is to be considered
hence, all other options are incorrect