Final answer:
Paragraph 8 is included to introduce another method of dolphin communication, particularly through sound which is vital for various functions in the animal kingdom, from mating calls to echolocation.
Therefore, the option B is correct.
Step-by-step explanation:
The author included paragraph 8 in the article, which begins with "Sound, though important in dolphin communication...", to introduce another method by which dolphins communicate. Sound plays a crucial role in the communication among dolphins, just as it does in the animal kingdom at large, where vocalizations can serve multiple functions such as attracting mates, as male crickets do, or locating prey and navigating through echolocation, as seen in dolphins and bats. Infrasound is used by elephants and whales for long-distance communication due to its low-frequency waves, which can travel great distances underwater or through the ground.