17. 要求修改信用证的计价方法

your order has been accepted on fob basis.

your l/c is described as basis and some differences will be made between the invoice amount and the amount of you require.

therefore please amend the price of your l/c to fob basis.

18. 由于船位不足， 请求延长信用证的期限

in spite of our effort， we find it impossible to secure space for the shipment owing to the unusual shortage of shipping space.

please allow us to request that you extend your l/c to April 10.

19. 答应延长信用证的期限

as requested in your letter of April 10， we have instructed our bankers to extend the l/c no. 1025 up to and including October 31.therefore you will receive the extension advice by this weekend.