German or Austrian subway system, 1938 (originally in reference to Berlin), from German U-bahn, short for Untergrund-bahn, literally "underground railway."
例句
1. The United States of America is commonly abbreviated to U.S.A.. 美利坚合众国常被缩略为U. S. A..
2. Somebody forgot to bring along the U-bolts to clamp the microphones to the pole. 有人忘了带把麦克风固定在支架上的U形螺栓。
3. And what of the effect on U.S domestic opinion? 对美国国内的舆论有什么影响?
4. U.S. forces now occupy a part of the country. 美国军队现在占领了该国的一部分。
5. Hammer's business pedigree almost gua-ranteed him the acquaintance of U.S. presidents. 哈默的商业背景几乎保证了他能够结识美国总统。