单选题 You ______ him out though you were very busy.
A. could have helped B. must help
C. should have helped D. ought to help

【正确答案】 C
【答案解析】[解析] should have done sth．意为：本应该做某事(但却没有做)，这句话的意思是“尽管你很忙，但是你(本)应该帮助他摆脱困境。”