Everyone makes mistakes in life, but for whales and dolphins, the "mistake" of landing on the shore costs the highest price---their lives. People living along the coast of Australia and New Zealand have been shocked and saddened by the number of whales and dolphins that they have found on their beaches recently. Since November 28th, 96 whales and dolphins have died in Australia and 53 whales died in New Zealand. Although 20 whales were saved, some of these were not expected to live, as they were too weak to swim with the others back to sea. Bob Brown, leader of Australia's Green party, said the mass beaching was caused by the recent "sound bombing" of the ocean floor between the two countries. This is a method of testing for oil and gas reserves  . But mass beaching of whales has long puzzled scientists. Typically most members of the stranded   group will appear to be perfectly healthy. "Some researchers believe that close relationship within the group causes the problem, if one gets into trouble, the others will not leave" said Shery Gibney, a leading biologist in New Zealand. "Some will come in and try and assist it; if they get trapped on the beach, then more will come." Another common theory is that the whales' navigation   system are thought to break down in some way. It has been said that whales follow electromagnetic   patterns in the sea-bed. The whales can get confused because these patterns sometimes change. That would be a bit like a new roundabout   being built on a road you were used to driving on. You might be confused for a minute when you come to it for the first time, and you might even take a wrong turning before getting back on your route. A different idea is that when whales chase fish for food they end up in shallow waters because they are not paying attention to where they are going. And yet, from time to time a group will swim on purpose into shallow waters and end up on the beach, where they die. If returned to the sea, some whales often show great determination in restraining themselves. Which of the following can be used to explain the term "sound bombing"?
The terrible sound that is caused in the war between two countries. Human activities that aim to explore the ocean floor. The loud sound that whales and dolphins make. The earthquakes that happen on the ocean floor.