问题补充：
Your advice was a great help to us, without which all our efforts .
A. wouldn’t pay off
B. hadn’t paid off
C. wouldn’t have paid off
D. didn’t pay off
答案：
A. wouldn’t pay off
B. hadn’t paid off
(答案→)C. wouldn’t have paid off
D. didn’t pay off
解析：考查虚拟语气。根据前面的was和句意可知本题是一个由without引导的与过去事实相反含蓄条件句，使用情态动词+have done的形式。句意：你的建议对我们很有益，要是没有你的建议，我们的努力就不会得到回报。
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