Which of these illustrates that sound waves can travel through a liquid? a. voices can be heard as people speak to one another b. whales and porpoises signal each other by making sounds c. astronauts can’t hear each other in space unless they use a radio d. footsteps can be heard through the ceiling as someone walks on the roof

B. Whales and porpoises signal each other by making sounds

Explanation:

Sound is a type of mechanical wave, which consists of oscillations of the particles in a medium. It is also classified as longitudinal wave, which means that the direction of the oscillation of the particles in the medium is parallel to the direction of propagation of the wave, forming alternating regions of higher particle density (compressions) and lower particle density (rarefactions).

Since sound is a mechanical wave, it just need a medium to propagate through. Therefore, it can travel through solids, liquids and gases.

In particular, the option

B. Whales and porpoises signal each other by making sounds

is an example of this: these animals emit ultrasound waves (a type of sound waves with high frequency), that travel through the water, and then are reflected back to the animal, allowing the animal to understand the distance of the object from which the wave has been reflected back.

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