信用证是国际银行业务中最广泛使用的一种凭证。信用证由来已久，卓有成效，是促进国际贸易的一种手段，在经济与政治不稳定时期尤其如此。
【正确答案】：The letter of credit is the most widely used instrument of international banking. It has had a long and successful history as a means of facilitating international trade particularly during times of economic and political uncertainty.
