按《公约》规定，下面属于发盘的生效条件的选项有：
A. 发盘一经发出即生效
B. 发盘于送达受盘人时生效
C. A & B
下列哪一个选项正确表达了发盘的有效期？
A. We will keep this offer open for 10 days.
B. This offer will be available until 23rdof March.
C. A & B
下列哪一个邮件内容符合《公约》中关于发盘撤回/撤销的规定？
A.Thanks for your acceptance. Yet it’s a regret that we have to cancel this offer due to the dramatic rising of iron cost in the international market yesterday.
B. A.We’ve not yet received any of your message upon acceptance of our last offer mailed to you last Friday. Yet it’s a regret that we have to cancel this offer due to the dramatic hiking of iron in the international market yesterday.
以下哪一项不是发盘效力终止的原因？
A. 被受盘人拒绝
B. 被受盘人还盘
C.发盘人撤销该发盘
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