Scientists have found further evidence that dolphins call each other by "name".

Research has revealed that the marine mammals use a unique whistle to identify each other. A team from the University of St-Andrews in Scotland found that when the animals hear their own call played back to them, they respond.

Dr. Vincent Janik, from the university's Sea Mammal Research Unit, said, "Dolphins live in this three-dimensional (三维) environment, offshore without any kind of landmarks and they need to stay together as a group. These animals live in an environment where they need a very efficient system to stay in touch. "

It had been long suspected that dolphins use distinctive whistles in much the same way that humans use names. Previous research found that these calls were used frequently, and dolphins in the same group were able to learn and copy the unusual sounds. But this is the first time that the animals' response to being addressed by their "name" has been studied. To investigate, researchers recorded a group of wild bottlenose dolphins, capturing each animal's signature sound. They then played these calls back using underwater speakers.

“We played signature whistles of animals in the group; we also played other whistles in their repertoire (曲目) and then signature whistles of different populations-animals they had never seen in their lives," explained Dr. Janik.

The researchers found that individuals only responded to their own calls, by sounding their whistles back. The team believes the dolphins are acting like humans: when they hear their names,   they answer.

Dr. Janik said this skill probably came about to help the animals to stick together in a group in their vast underwater habitat. He said, "Most of the time they can't see each other, they can't use smell underwater, which is a very important sense in mamma is tor recognition, and they also don't tend to hang out in one spot, so they don't have nests or burrows that they return to.”

【小题1】How can the marine mammals distinguish their group members?

A．By using a special whistle.	B．By using special gestures.
C．By speaking special languages.	D．By different means of swimming in the sea.

【小题2】What similarities are there between dolphins and humans?

A．They can answer while being called.

B．They can express their feelings with words.

C．They can perform different whistles.

D．They can live individually or in groups.

【小题3】How do dolphins live better in the underwater habitat?

A．See each other clearly.

B．Use the smell underwater.

C．Have nests and get back regularly.

D．Call each other by name and make response.

【小题4】What topic is the passage most related to?

A．Protecting natural environment.

B．The scientific discoveries.

C．The development of scientific technology.

D．The harmonious relationship between man and animals.