acceptance shall reach the offeror within the time limit prescribed in the offer. 承诺应当在要约确定的期限内到达要约人。 Where no time limit is prescribed in the offer, the acceptance shall reach the offeror in accordance with the following provisions: (1) If the offer is made in dialog, the acceptance shall be made immediately. (2) If the offer is made in forms other than a dialog, the acceptance shall reach the offeror within a reasonable time limit. 要约没有确定承诺期限的，承诺应当依照下列规定到达： （一）要约以对话方式作出的，应当即时作出承诺； （二）要约以非对话方式作出的，承诺应当在合理期限内到达。 A contract is formed when the acceptance becomes effective,except as otherwise provided by the law or agreed by the parties. 承诺生效时合同成立，但是法律另有规定或者当事人另有约定的除外。