An offer is a declaration of will to contract with another person, and the declaration of will shall meet the following conditions: (1) Its contents shall be specific and definite. (2) It indicates that the offeror will be bound by the declaration of will in case of acceptance by the offeree. 要约是希望与他人订立合同的意思表示，该意思表示应当符合下列条件： （一）内容具体确定； （二）表明经受要约人承诺，要约人即受该意思表示约束。 An offer may be revoked, except under any of the following circumstances: (1) The offeror explicitly states, by fixing a time limit for acceptance or otherwise, that the offer is irrevocable. (2) The offeree has reasons to believe that the offer is irrevocable, and has made reasonable preparation for performing the contact. 要约可以撤销，但是有下列情形之一的除外： （一）要约人以确定承诺期限或者其他形式明示要约不可撤销； （二）受要约人有理由认为要约是不可撤销的，并已经为履行合同做了合理准备工作。