China's tit-for-tat import taxes on some American goods came into effect on Monday, as the trade war between the world's two biggest economies escalates and US President Donald Trump threatens to hit more countries with tariffs. 随着世界两大经济体之间的贸易战不断升级，美国总统唐纳德·特朗普威胁对更多国家征收关税，中国对部分美国商品征收针锋相对的进口税于周一生效。