The lightning strikes and causes the power lines to about 6,000 volts and damage a server. Which of the following power instability do it describes?

A.
Harmonic distortion

B.
Sags

C.
Brownouts

D.
A spike

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:
A: Harmonic distortion is a deformation of the normal electrical power waveform.
B: Power sags are short-term, low-voltage conditions, produced by power utilities unable to meet demand C: A brownout is a reduction in line voltage for an extended time period, ranging from a few minutes to a few days.
References:
Charles J. Brooks, Server+ Certification Exam Cram 2 (Exam SK0-002), QUE Publishing, Indianapolis, 2006, pp. 227-240.