A． Each part has a different meaning．

B． So they cannot create as many numbers as we can．

C． That's because China has the longest mobile phone numbers in the world．

D． Also， mobile phone numbers can be recycled．

E． The main reason for using 11 digits is that we have the largest population in the world．

Have you ever counted the number of digits（数字） in your mobile phone number？ Your number has 11digits． You may sometimes find it hard to remember your number． （1） 　　Why is that？

The 11digits can be divided into three parts． （2） 　　The first three numbers tell you which mobile phone service provider you are using． For example， 135 is for the China Mobile Communication Corporation and 188 is for China Unicom． The fourth to the seventh digits tell you which area the number is recorded in． And the last four digits are random （随机的）．

（3） 　　We once had 10numbers． But as our population grew， there were not enough numbers for us to use． So we began to use 11digits starting from 1999．

Eleven digits can be used to make tens of billions of mobile phone numbers， according to the Xinhua News Agency． That's enough for each person to have seven or eight phone numbers to use in China（4） 　　Usually， the service provider will reuse a canceled number after three to six months． If you call a number that you haven't contacted （联络） for a long time， you may find that its owner has changed．

Besides China， Britain and Japan also use 11﹣digit mobile phone numbers． But their numbers always start with 0． （5） 　　Countries like the United States， Australia and India use phone numbers with l0digits． Canada's mobile phone numbers are perhaps the world's shortest： they use seven digits．