We have received your letter of September 12，（）we are glad to know that you are interested in our electric heaters. which。 at which。 from which。 in which。
We are（）to have your enquiry for Sewing Machines. please。 pleased。 pleasure。 in pleasure。
We have to point out that the postponement of the fulfilment of the contract（）caused us certain expenses. had。 have。 has。 having。
We（）the seminar sponsored by you in September last year. aware。 aware of。 are aware of。 are aware。
短文互译：From Chinese into English在国际贸易中买卖双方距离遥远，业务成交与实际交货时间相隔较长，付款问题远比国内贸易复杂。卖方总希望在收到货款后发货，而买方总希望收到货物后付款。所以国际贸易中，一般采用信用证付款方式，使买卖双方的利益都得到一定的保障。
We shall do everything possible to assist you in（）a mutually beneficial trade.
