Though I was tired out that evening, I from falling asleep by the great pain in my knee.A

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(答案→)A. was prevented
B. had prevented
C. has prevented
D. am prevented
解析：考查时态语态：句意：虽然我那天晚上很累，膝盖上的疼痛让我不能入睡。从Though I was tired out that evening,可知是一般过去式，而且I和prevent是被动关系，选A。