An automobile originally purchased for $18,000 is losing value at a rate of 15% per year. The number of dollars it will be worth 5 years after purchase is 18,000(0.85)^5. Rewriting the expression 18,000(0.85)^5 in which of these ways would be useful in calculating the rate at which it is losing value per month?

A. 18,000(0.85^1/12)^60
B. 18,000(0.85^12)^60
C. 18,000(0.85^60)^1/12
D. 18,000(0.85^60)^12