应该是in the USA，美国是一个特定的词组.不能少了定冠词the.在国家的全名之前都要有the,比如in the PRC(在中国）,in the Swiss Confederation (在瑞士）.如果是非正式口语名字,比如 in America,in China,in Switzerland就不用.例如：Any holiday in the USA and Canada is enhanced by renting a self-drive car.租车自驾绝对会使在美国和加拿大的度假更加愉快。That's a general British failing. In the USA it's quite different.那是英国人的普遍缺点。在美国，情况就大不一样了。In the USA, most people love American football and basketball the most.在美国，绝大部分人都最喜欢美式橄榄球和篮球。
