Don't give a business gift ____.

(A)until you reveive ..

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以下為英英的解釋
【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.

中文翻譯：不要給商業禮物，直到你收為一個為止！

在選項中，只有unil具有否定的味道，其他的都沒有！故答案選a！