问题补充：
It was not a good idea to go skating. You your leg.
A. can break
B. could break
C. could have broken
D. could have been broken
答案：
A. can break
B. could break
(答案→)C. could have broken
D. could have been broken
解析：本题关键为抓住题中提供的信息。“It was not a good idea’表明动作发生于过去，情态动词后接动词完成式表明对过去动作的猜测。
