听力原文： Secretary-General Kofi Annan has issued a call for renewing the mission of the United Nations on the 60th anniversary of its founding. A simple anniversary observance at U.N. headquarters was in contrast to the more elaborate ceremonies a day earlier in San Francisco. A brief, but moving, ceremony in a virtually empty General Assembly hall marked the world body's 60th birthday. A group of U.N. tour guides read the preamble to the organization's charter in English and French, followed by a brief statement from Secretary-General Annan. 'The words we have just heard, the words of the preamble of our Charter, are engraved on the collective memory of mankind. Over 60 years, the United Nations has striven to redeem those pledges. Where we could we have averted the scourge of war. Where we could not, we have sought to resolve conflict and build peace.' The secretary-general noted the world body's many successes, including keeping the peace, helping in the fight against smallpox and polio, helping with elections in many countries, and bringing relief to victims of disasters such as last December's Indian Ocean tsunami. But Mr. Annan noted that not every undertaking has been a success. 'We have also had failures. The worst, perhaps, was our collective failure to prevent genocide in Rwanda.' The ceremony closed with a song of peace sung by the United Nations Singers. The entire event took less than half an hour. The observance came a day after dozens of international leaders gathered for a more elaborate ceremony in San Francisco, where the U.N. Charter was signed in 1945. The United States was represented at the San Francisco celebration by its representative to the U. N. Economic and Social Council, Ambassador Sichan Siv. Further observances are set for September, when world leaders gather in New York to mark the opening of the 60th General Assembly session. Mr. Annan noted many successes of the United Nations, except ______.