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云南省楚雄市2017高考英语完形填空、阅读理解一轮基础训练（11）及答案 【广东卷完形填空】 Number sense is not the ability to count. It is the ability to recognize a 1 in number. Human beings are born with this ability. 2 ，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 3 . However, if you remove two, the bird 4 leaves. This means that the bird knows the 5 between two and three. Another interesting experiment showed a bird's 6 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 7 until the man left the tower. The man had an 8 .He took another man with him to the tower. One man left and the other stayed, but they did not 9 the bird. The crow stayed away until the second man left, too. The experiment was | 
