An equipment bought four years ago for $4,230 has a current market value of $1,850. If kept for one more year, it will cost $1,170 in operation and maintenance costs and will have a market value of $1,420 at the end of the year. In conducting a replacement analysis for the equipment, which of those cash flows can be considered a sunk cost?
A. $1,170
B. $4,230
C. $1,850
D. $1,420