问题补充：
If it for the snow, we the mountain yesterday.
A. were not; could have climbed
B. were not; could climb
C. had not been; could have climbed
D. had not been; could climb
答案：
A. were not; could have climbed
B. were not; could climb
(答案→)C. had not been; could have climbed
D. had not been; could climb
解析：句意：假如天气昨天没有下雪，我们就已经爬上了那座山峰。if引导的从句对过去情况的虚拟推测，从句用had done，主句用would/should/could+have +done,故选C
