Just like humans，birds too rely on sound to communicate.However，they do not have a "language" in the true sense of the word and instead produce a variety of sounds to convey different emotions.
   Often，birds recognize their mates（or young） by sound rather than sight.Hungry young birds use begging calls to let their mothers know it is feeding time.Alarm calls，flight calls and warning calls are other sounds made frequently by adults.
   Anew study shows that songbirds rehearse（排演） their songs even in their sleep.The activity in the brain of the birds when asleep is similar to the brain activity when the birds were awake and singing.The team used tiny recording devices to measure the activity of individual brain cells in four songbirds both when they were singing and when they were asleep.
   Apparently the bird stores a song after hearing it，and then rehearses it later in is sleep.Scientists now believe the birds "dream of songs and tunes" to help them master the fine art of singing and that sleep plays a key role in the learning process!
   Many songbirds learn to sing listening to adult birds of the same species.However，if separated from the adults，the young birds develop sounds which are hard to understand instead of normal song patterns.Researchers carried out an experiment in which a male bullfinch（灰雀）was raised by a female canary（金絲雀）.The bullfinch soon learned the canary's song and when it was later mated to a female bullfinch，Mr.Bullfinch taught his children the canary's songs.
   Last year，a British survey of London's songbirds showed that the city's birds are losing their tunes.Birds could hardly hear one another，over the traffic noise；as a result，instead of copying the sweet notes of the adults，young birds were copying the sounds they heard most often ，namely car horns and beeping cellphones!

（1）According to the passage，birds recognize their mates by

B

B

.
A．using their own words
B．listening to their sounds
C．looking at their appearances
D．singing the same songs
（2）What does the story of Mr.Bullfinch suggest？

A

A

A．young birds learn to sing from whom they live together with.
B．birds only learn how to sing from the same adult species.
C．it's not easy for adult birds to teach young birds songs.
D．a(chǎn) canary's song is more beautiful than a bullfinch's.
（3）What can we infer from the last paragraph？

D

D

A．traffic noise makes young birds become deaf.
B．birds in the city can sing as sweetly as those in the wild.
C．birds in the city recognize their mates mainly by sight.
D．noise pollution causes much trouble for birds in the city.
（4）What does the author mainly intend to tell the readers with the text？

B

B

A．To inform the readers how songbirds bring up their babies.
B．To explain to the readers how songbirds communicate with each other.
C．To persuade the readers to reduce the noise pollution and protect the birds.
D．To show the differences in songbirds' brain activities when they are awake and asleep.