【正确答案】 A

【答案解析】would have done可表示与过去事实相反的假设的结果，例如：If I had had themoney last year，I would have bought a house．如果去年我有了这笔钱，我就会买一所房子了。If he had discovered the secret，he would have been surprised．假如他发现了这个秘密，就会感到惊讶的。但是，有时虚拟条件并不通过条件从句表达出来，而是隐含在上下文中，例如：I was away that day．Otherwise，I would have attended the lecture．那一天我不在家，否则我会去听演讲的。Make any noise，and you would be discovered．只要一出声就会被发现。因此答案是A。