付款条件的英文表达 — 国际贸易填空题
题目
某出口公司向英国客户出售一批纺织品，合同规定：买方须在收到卖方形式发票后7个工作日内，以不可撤销的即期信用证开到我方，信用证议付有效期为装运期后第15天在中国到期。请补全该付款条款英文表述中的空位（每空一词）：Payment shall be made by an ____ L/C ____ sight, to reach the Sellers within 7 working days after receipt of the Sellers' proforma invoice, and shall remain valid for negotiation in China until the 15th day after the date of shipment.