Darwin noted that some human emotional expressions might have started as part of a physiological function：for example，exposing the teeth to bite food．The function，however，took on meaning and became a form of communication which signals anger．
   The same may be true for the animals．Baby monkeys cry for attention．They also cry to signal to an adult that they want to be carried． "Chimpanzees do make upset voice when they are being weaned（斷奶） by their mothers or have lost their mothers or another individual，" says Anne Pusey，a professor at the University of Minnesota． "They whimper （嗚咽） and cry and scream．When we hear these calls，the emotion involved seems obvious．However，they do not weep in the sense of producing tears．I have seen an adolescent male whimpering when he lost sight of his older brother with whom he had been traveling．"
   Babies of many mammalian species，including rats，cry．Moreover，when a baby rat cries，often his mother brings the fallen pup back into the nest．This is probably a straightforward communication，as it is with humans．However，psychologists at the University of Iowa aren't convinced．
   The Iowan researchers can cause the same crying sounds by producing large decreases and then increases in blood flow．The blood flow also goes down when baby rats get cold．Thus，they conclude baby rats cry in the same way that we sneeze．Of course the rat baby could be crying because he's cold and wants his mother to know．
   "All young mammals make cries when separated from their mother，" says Jaak Panksepp，a
psychologist at Bowling Green State University． "If you're willing to call this crying，then certainly other animals show this emotional response．" he says， "Some of us take seriously that animals do have emotions．"

（1）According to the first paragraph，what kind of emotion does "exposing the teeth" express？

C

C

A．Disappointment．
B．Excitement．
C．Anger．
D．Happiness．
（2）Which is one probable reason why young chimpanzees might be crying？

D

D

A．They meet their brother．
B．They have nothing to eat．
C．They are being breast-fed．
D．They are parted from their mother．
（3）Under what circumstance will baby rats cry just like humans' sneeze？

B

B

A．Their blood flow is decreased．
B．They feel cold and long for affection．
C．Their blood flow is increased．
D．Their mother brings them back home．
（4）Where is the passage most likely taken from？

A

A

A．An animal journal．
B．A physiology book．
C．A health magazine．
D．A cultural newspaper．