Which of the following is a very high voltage level usually twice the normal voltage?

A.
A spike

B.
Sags

C.
A surge.

D.
Brownouts

Explanation:
A spike is a very high voltage level-usually twice the normal voltage-that is supplied for an instant (usually in the millisecond range), and can be deadly for servers.

Incorrect Answers:
B: Sags are short periods of time when the supply voltage is low.
C: A surge is a voltage increase (10 or 20 volts above normal) that occurs over a longer period of time D: Brownouts occur over longer periods of time (several seconds or longer).
References:
Charles J. Brooks, Server+ Certification Exam Cram 2 (Exam SK0-002), QUE Publishing, Indianapolis, 2006, pp. 227-240.