Talk to the animals
All kinds of animals can communicate in one way or another． Maybe you have heard about the way bees dance around to send messages to each other and the ways dogs bark （犬吠） to give warnings or to be friendly． But did you know about infrasonic （次声的） communication
used by elephants？ This is how it works：
Humans hear low sounds like the thunder rumbling （隆隆作响） in the sky． But we don't hear sounds lower than that． However， animals such as elephants can hear much lower sounds than humans can． And what's more， they can make lower sounds as well， and they use them to communicate with each other． This is known as infrasound．
The amazing thing about infrasound is that it travels over several kilometers． Sounds which have a higher pitch （音高）， like the ones people can hear， don't travel well through walls，
leaves， trees， and so on， which is why we can't hear sounds from more than 100meters away． But infrasound is much "stronger"， and things like trees have no effect on it． Therefore it can travel much further． Elephants can hear infrasonic calls from 4kilometers away!
There have been reports of people watching groups of elephants feeding or resting and then the elephants suddenly all stopped whatever they were doing for no reason at all． They obviously heard a warning call from a long way away， but the people didn't hear a sound． In places like a zoo or wildlife park where you can get nearer to animals， it is easier to sense when infrasonic sounds are made． When you stand near mother elephants with their babies in a zoo you may notice a slight rumbling in the air every few minutes - not loud or strong， but clearly noticeable． This is infrasonic communication - the mother elephants "talking" to their babies．

(1) How do elephants communicate with each other？ ______
A．By dancing around to send messages．
B．By using infrasonic communication．
C．By different sounds of rumbling．
D．By different ways of barking．

(2) What is the amazing thing about infrasound？ ______
A．It goes into the sky．
B． It travels very far．
C． It sounds stronger．
D． It stops at walls．

(3) Humans can hear ______ ．
A．sounds with a higher pitch
B．sounds from 100meters away
C．lower sounds than elephants can
D．lower sounds than thunder rumbling

(4) In places like zoos， ______ ．
A．elephants don't need to make infrasonic sounds
B．it is easier for elephants to make infrasonic sounds
C．mother elephants don't let people stand near their babies
D．humans can sense infrasonic sounds when they are made