`1.` can be understood

`2.` are usually clearly defined

`3.` have been fought

`4.` is called

`5.` was reared

`6.` is determined

`7.` may be divided

`8.` are allowed

1) can be understood                2) are usually clearly defined

3) have been fought                  4) is called

5) was reared                             6) is determined

7) may be divided                      8) are allowed

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Thousands of books have been written about the territorial instinct of animals. Humans are territorial too and when we understand this, some kinds of aggressive behaviour (1)can be understood  more easily. Every country is a territory with boundaries which (2) are usually clearly defined usually clearly . Within each country there are smaller territories: counties and cities. Throughout history wars (3) have been fought    by people protecting the territory in which they live. However, there are other kinds of territory as well. One such territory (4) is called“personal space”. For animals, the size of this space depends on the conditions in which the animal (5) was reared  , whether in the wild or in a zoo. For humans, it depends on the density of the population in the place where they grew up. To some extent, the size of an individual’s personal space (6) is determined by their culture. Personal space (7) may be divided into four zones: the intimate, personal, social and public zones. The intimate zone extends fifteen to forty-five centimetres from the body. Only close friends and relatives (8) are allowed to enter the intimate zone. If a stranger enters it, the individual becomes anxious and may feel threatened.