Where an offer is made by letter or telegram, the time limit for acceptance shall accrue from the date shown in the letter or from the date on which the telegram is handed in for dispatch. If no such date is shown in the letter, it shall accrue from the postmark date on the envelope. Where an offer is made by means of instantaneous communication, such as telephone, facsimile or email, the time limit for acceptance shall accrue from the moment that the offer reaches the offeree. 要约以信件或者电报作出的，承诺期限自信件载明的日期或者电报交发之日开始计算。信件未载明日期的，自投寄该信件的邮戳日期开始计算。要约以电话、传真、电子邮件等快速通讯方式作出的，承诺期限自要约到达受要约人时开始计算。 If notice of acceptance is not required, the acceptance shall become effective when an act of acceptance is performed according to the usage of trade or as required in the offer. 承诺不需要通知的，根据交易习惯或者要约的要求作出承诺的行为时生效。