Not until the exam the importance of doing homework.
A. had he failed; he realized
B. he had failed; did he realize
C. he had failed; he realized
D. had he failed; did he realize
网友回答
A. had he failed; he realized
(答案→)B. he had failed; did he realize
C. he had failed; he realized
D. had he failed; did he realize
解析：可联系答.案.网客服索取。