(2018·山东临沂)Have you ever counted the number of digits (数字) in your mobile phone number? Your number has 11 digits. You may sometimes find it hard to remember your number. That’s because China has the longest mobile phone numbers in the world. Why is that?

　　The 11 digits can be divided into three parts. Each part has a different meaning. The first three numbers tell you which mobile phone service provider (提供者) you are using For example, 135 is for China Mobile Communications Corporation and 188 is for China Unicom. The fourth to the seventh digits tell you where the number is registered (注册). And the last four digits are random (随机的).

　　The main reason for using 11 digits is that we have the largest population in the world. We once had 10 numbers. But as our population grew, there were not enough numbers for us to use. So we began to use 11 digits starting from 1999. Eleven digits can be used to make tens of billions of mobile phone numbers. That’s enough for each person to have seven or eight phone numbers to use in China.

　　And mobile phone numbers can be recycled. Usually, the service provider will reuse a canceled number after three to six months. If you call a number that you haven’t contacted (联系) 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. So they cannot create as many numbers as we can. Countries like the United States, Australia and India use phone numbers with 10 digits. Canada’s mobile phone numbers are perhaps the shortest in the world: they use seven digits.