Your lead mechanical technician has reported that one of the three rooftop HVAC units on your company's data center is likely to fail within the next six months. There are four possible replacement units that he has evaluated. All the units have comparable reliability and performance. Using a 5-year planning horizon, which unit should be purchased? A. Unit A because it can be on site quickest and has a useful life over 5 years. C. Unit C because it has the fastest delivery/efficient annual operating cost/longest expected life combination. D. Unit D because it is the highest quality system for this mission-critical facility. B. Unit B because it has the lowest initial cost of the unit