What is the most important element that you should consider when purchasing a UPS?

A.
The power rating of the UPS.

B.
The cost associated with purchasing the UPS.

C.
The amount of space needed to install the UPS.

D.
The support agreement of the vendor.

Explanation:
The power rating of the UPS, measured in Volt-Amps (VA), is the most important element that you should consider when purchasing a UPS. The power rating of the UPS would indicate whether or not the UPS has the necessary capacity to support your servers during power failures.
References:
Charles J. Brooks, Server+ Certification Exam Cram 2 (Exam SK0-002), QUE Publishing, Indianapolis, 2006, pp. 431-433.