单选题 According to the rules of the factory, you mustn't ask for leave ______ you have a doctor's note.

【正确答案】 A
【答案解析】[考点] 词义辨析
[解析] unless意为“如果不,除非”;on condition that意为“如果”;though意为“尽管”;until意为“直到……才”。根据题意选A。