alleryAn echo is a:
AA high-frequency sound only
BA type of light
CSound reflected from a distant surface and heard again
DSound created from nothing
Answer & Solution
Correct answer: C. Sound reflected from a distant surface and heard again
Echo = sound reflected from a distant hard surface, returning to the listener.
To be heard as a SEPARATE sound, the echo must arrive at least 0.1 s after the original (this is why echoes need a minimum reflector distance of about 17 m in air).
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