In Southeast Asia, ______.

参考解析：

细节理解题。根据第三段最后一句“Cash on delivery is still prevalent, and other local players are in the fray”可知，货到付款仍然盛行，其他本地商家也在争抢，因此可推断A项正确。根据第六段第一句“Amazon so far counts Singapore as its only Southeast Asian market, though industry experts widely expect it will expand into other countries.”可知，到目前为止，亚马逊将新加坡视为其唯一的东南亚市场，不过业内专家普遍预计，它将向其他国家扩张。因此B项（电子商务到达顶峰）错误。根据第九段第五句“Alibaba has a long lead over Amazon and is building up its infrastructure across Southeast Asia.”可知，阿里巴巴长期领先亚马逊，并正在东南亚建立基础设施。因此C项错误。根据第十段最后一句“Competing in the market is likely to be expensive, thanks to customer price cuts and rebates in addition to expansion costs.”可知，由于客户的降价和回扣以及扩张成本，在这个市场上竞争的成本可能会很高。因此D项错误。故选A。