题目内容
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？
查看答案
搜索结果不匹配？点我反馈
更多问题
大众媒介影响（）
A．20Hz～2K．HzB．100Hz～1KHzC．20Hz～20KHzD．20Hz～200KHz
日化厂因扩大规模资金紧张，向耐火材料厂借款480万元，借期半年，利息6万元。签订了借款合同。该合同应缴纳印花税240元。()
Designing a lens can be compared to playing chess. In chess a player tries to trap his opponent' s king in' a series of moves. On creating a lens, lens designers attempts to "trap" light by forcing all the rays arising from a single point in the subject to converge on a single point in the image, as a consequence of their passing through a series of transparent elements with precisely curved surfaces. Since in both cases the ultimate goal and the means by which it can be attained are known, one is tempted to think there will be a single best decision at any point along the way. The number of possible consequences flowing from any one decision is so large, however, as to be virtually, if not actually, infinite. Therefore in lens design, as in chess, perfect solutions to a problem are beyond reach. The same principles apply to all lenses.
The lens designer has one enormous advantage over the chess player. The designer is free to call on any available source of help to guide him through the countless number of possibilities. Most of that help once came from mathematics and physics, but recently computer technology, information theory, chemistry, industrial engineering and psychophysics have all contributed to making the designer' s job immeasurably more productive. Some of the lenses on the market today were inconceivable a decade ago. Others whose design is as much as a century old can now be mass-produced at low cost. With the development of automatic production methods, lenses are made by the millions, both out of glass and out of plastics. Today' s lenses are better than the best lenses used by the great photographers of the past. Moreover, their price may be lower, in spite of the fact that the 19th century craftsmen worked for only a few dollars a week and today' s lenses are more complex. The lens designer cannot fail to be grateful for the science and technology that have made his work easier and his creations more widely available, but he is also humbled: it is no longer practical for a fine photographic lens to be designed from beginning to end by a single human mind.
In what way does lens design resemble chess？
微信支付 
支付宝支付