Question

Define
a) Echo
b) infra Sound.​

Answer 1

Answer:

a) An echo answer or echo response is a way of answering a polar question without using words for yes and no. The verb used in the question is simply echoed in the answer, negated if the answer has a negative truth-value.

b) Infrasound, in its popular definition as sound below a frequency of 20 Hz, is clearly audible, the hearing threshold having been measured down to 1.5 Hz.  Investigations of complaints of low-frequency noise often fail to measure any significant noise.

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