Number sense is not the ability to count. It is the ability to recognize a 14 in number. Human beings are born with this ability. 15 , experiments show that many animals are, too. For example, many birds have good number sense. If a nest has four eggs and you remove one, the bird will not 16 . However, if you remove two, the bird 17 leaves. This means that the bird knows the 18 between two and three.
Another interesting experiment showed a bird's 19 number sense. A man was trying to take a photo of a crow(乌鸦)that had a nest in a tower, but the crow always left when she saw him coming. The bird did not 20 until the man left the tower. The man had an 21 . He took another man with him to the tower. One man left and the other stayed, but they did not 22 the bird. The crow stayed away until the second man left, too. The experiment was 23 with three men and then with four men. But the crow did not return to the nest until all the men were 24 . It was not until five men went into the tower and only four left that they were 25 able to fool the crow.
How good is a human's number sense? It's not very good. For example, babies about fourteen months old almost always notice if something is taken away from a 26 group. But when the number goes beyond three or four, the children are 27 fooled.
It seems that number sense is something we have in common with many animals in this world, and that our human 28 is not much better than a crow's.
14. A. rise B. pattern C. change D. trend
15. A. Importantly B. Surprisingly C. Disappointedly D. Fortunately
16. A. survive B. care C. hatch D. notice
17. A. generally B. sincerely C. casually D. deliberately
18. A. distance B. range C. difference D. interval
19. A. amazing B. annoying C. satisfying D. disturbing
20. A. relax B. recover C. react D. return
21. A. appointment B. excuse C. idea D. explanation
22. A. fool B. hurt C. catch D. kill
23.A. reported B. repeated C. designed D. approved
24.A. confused B. gone C. tired D. drunk
25.A. gradually B. luckily C. strangely D. finally
26.A. single B. small C. local D. new
27. A. seldom B. temporarily C. merely D. often
28. A. sight B. nature C. ability D. belief