问题补充：
he met with the difficulty did he realize the importance of our help.
A. Even though
B. Never until
C. Only before
D. Ever since
答案：
A. Even though
(答案→)B. Never until
C. Only before
D. Ever since
解析：此题考查从句的引导词。根据主句是倒装did he realize可以排除A、D两项。如果选C项，则主句应该用过去完成时态had he realized,因而被排除。
