Don't give a business gift ____.

(A)until you reveive ..

访客只能看到部份内容，免费 加入会员 或由脸书 Google 可以看到全部内容

以下为英英的解释
【not until】used to emphasize that something does not happen before a certain point in time or before something else has happened:

'Can I go out and play now?' 'Not until you've done your homework.'
It was not until 1972 that the war finally came to an end.

Don't give a business gift until you reveive one.

中文翻译：不要给商业礼物，直到你收为一个为止！

在选项中，只有unil具有否定的味道，其他的都没有！故答案选a！