Harmonics problem. A square wave of frequency f contains harmonics (sine waves) at f, 3f, 5f, 7f, ... . Suppose a system responds to frequencies in the range 20-40 kHz but is insensitive outside of this range.
EXAMPLE:
Imagine applying a square wave with f = 30 kHz to this system. What is the shape of the response?
[ a 30 kHz sine wave. ]
Imagine applying a square wave with f = 10 kHz to this system.

What is the shape of the response?
A. A 10 kHz sine wave
B. A combination of 20, 30 and 40 kHz sine waves
C. A 30 kHz sine wave
D. No response