听力原文： More than a quarter of the world adult population are still unable to read and write. They are called illiterates. A worldwide campaign to change this situation has been launched by the United Nations, and the year 1990 has been designated as International Literacy Year. The message from the United Nations is that illiteracy must be ended for the good of both the individual and Third World development. Illiteracy does more than limit an individual's freedom to live a full and independent life. Governments of Third World countries where 98 per cent of illiterates live, find their national development programs are being held back by an under-educated and illiterate work force. Illiteracy is not only a problem of the developing countries. Adults in western nations are often too ashamed to admit they can't read and write. Therefore, they are unable to go to classes to change the situation. The success of International Literacy Year will depend largely on the political will of governments to provide equal opportunities in education. Women make up 60 per cent of the world's adult illiterates. More schools are needed in rural areas and slums. But one of the biggest tasks now facing international organizations is how to persuade hundreds of millions of illiterates that learning to read and write will actually benefit them. What percentage of the world population is illiterate?