问题补充：
George would certainly have attended the meeting，.
A. if he didn’t get a flat tire
B. if the flat tire hadn’t happened
C. had he not had a flat tire
D. had the tire not flattened itself
答案：
A. if he didn’t get a flat tire
B. if the flat tire hadn’t happened
(答案→)C. had he not had a flat tire
D. had the tire not flattened itself
解析：表示对过去情况的假设，主句动词形式为would(should，could,might)+have+过去分词，条件句为过去完成式，if可以省略，但要把had提前主语前面。 B、 D的表达不符合英语表达习惯，所以C是正确答案。
