Consider the following statements about noise:

1.Decibels is the unit of measurement of noise pollution

2.A change from 40 to 80 dB is exactly double in loudness

3.Zero decibel is the threshold point for hearing

4.A jet plane is one of the highest-decibel sources of noise

A1, 2 and 3

B2 and 3

C1, 3 and 4 ✓ Correct

D1, 2, 3 and 4

Correct answer: (C) 1, 3 and 4

Explanation

The true set is Statement 1, Statement 3 and Statement 4, covering the unit, hearing threshold and a loudest source.

Statement 1 is right: the decibel is the unit for measuring noise.

Statement 2 is wrong: the decibel scale is logarithmic, meaning a jump from 40 to 80 dB far exceeds a doubling of loudness.

Statement 3 is right: zero decibel marks the threshold of human hearing.

Statement 4 is right: a jet aircraft ranks among the loudest noise sources, near 140 dB.

Prolonged exposure above about 85 dB can cause permanent hearing loss.

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