To a bystander, which property of a sound wave changes due to the doppler a. speed b. phase c. amplitude d. frequency

To a bystander, which property of a sound wave changes due to the Doppler? D. Frequency

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Hi! The answer is D. Frequency. Thin about it-- when you listen to a siren go by, when it hasn't passed you yet it has a low frequency, but once it passes you, you hear a higher frequency.

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Ithink is a because if say increased in electronegativity