1)Dolphins use a process called sonar to find their way and to find food. (2)They emit sound waves that bounce off
objects and return, giving the dolphin information about distance, size, and density. (3)Some scientists think the
dolphins can even "turn up" these sound waves and stun their prey. (4)They know that certain levels of sound waves
could easily kill a large squid in a matter of minutes. (5)If these scientists are correct, dolphins could easily kill each
other-yet they don't.
The sentence that best expresses the implied main idea is: