问题
选择题
Though the problems were all very hard, Kate kept on working on them she finally solved all of them. [ ]
A. before
B. until
C. when
D. after
答案
答案：B
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Though the problems were all very hard, Kate kept on working on them she finally solved all of them. [ ]
A. before
B. until
C. when
D. after
答案：B