听力原文： The Vietnamese Foreign Minister Nguyan Manh Cam has called for rapid progress towards a trade agreement with the United States. Mr. Cam met with secretary of state Warren Christopher during the first ministerial visit to Washington by a Vietnamese delegation since President Clinton’s decision to establish full diplomatic relations in July. Mr. Christopher announced that a team of senior officials will travel to Hanoi to begin negotiations on a comprehensive treaty, probably next month. But American officials have warned that a trade agreement won’t come quickly or easily. The BBC correspondent in Washington says there' ll be considerable pressure on Vietnam to further liberalize the economy, implement legal, reform. and allow open political participation. What can be learnt on U. S. -Vietnamese relations?