China’s restrictions on exports of crucial rare-earth metals and rare-earth magnets remain one of the most difficult unresolved issues as President Trump and Xi Jinping prepare to meet this week. 随着特朗普总统和中国国家主席习近平准备于本周举行会晤，中国对关键稀土金属和稀土磁铁的出口限制依然是最棘手的未决问题之一。…