A patent was purchased for $670,000 with a legal life of 20 years. Management estimates that the patent has an 12 year economic life. The entry to record amortization would include:

a. an increase in research and development expense for $670,000.
b. a decrease in patent for $55,833.
c. an increase in amortization expense for $33,500.
d. an increase in accumulated amortization for $670,000.