Wild elephants live in herds of 10 to about 50. The leader is usually a female. A herd can go through a forest quietly. It travels in a single line. It goes about 6 miles an hour. When frightened, it may run at about 25 miles an hour. When they reach water, elephants swim across. They are great swimmers.     Elephants eat grass, leaves, small branches, and bark. They particularly like the tender leaves on the top of trees. How do they get these leaves? They use their heads to knock trees down. They can easily knock down a 30-foot tree. Elephants also eat berries, mangoes, coconuts, corn, and sugar cane. They love salt. A wild male adult eats 500 to 600 pounds of food a day.     Many people want to find the graveyards   of elephants. There is a strong belief that such graveyards exist. Here is why. Bones and tusks of dead elephants have almost never been found. Searches have been made in forests. Grassy plains have been searched too. But neither bones nor tusks are found. Elephants don't live forever. Where are their bones? They don't just bury themselves. Here is one belief. When an elephant gets sick or old, it instinctively knows death is near. It leaves the herd. It goes off to a secret graveyard. The place is known only to elephants, and perhaps other animals, but not to humans. Obviously, such a graveyard would be filled with tusks. These were once very valuable. The objective of explorers was to find this "gold" mine. This graveyard belief may be a truth or a myth. But it is romantic. It would be nice if it were true. From the passage we can learn that   _  .
other animals know where elephants' graveyards are elephants bury themselves when their deaths are near people have found bones and tusks of dead elephants whether there are graveyards of elephants is still not known