答案：A

题目分析：考查虚拟语气用法区别。用otherwise的虚拟条件句中，前一部分是陈述语气，后一部分是虚拟语气。如：I ran all the way to school , otherwise I would have been late .我一路跑到学校，不然就迟到了。同时otherwise引导虚拟语气可以改写为if引导的虚拟语气，根据题干，I was ill that day,就可以改写为“if I had not been ill that day”,这是从句，那么主句谓语动词与过去事实相反故用“would have done”故A    正确。