The mixture of his improved self-confidence and never-ending efforts is ________ lies behind his rap...
2022-10-19 18:14:57 63次 2014-2015学年湖南株洲市高三上学期教学质量统测英语试卷（解析版） 单项填空 反馈错误 加入收藏 正确率 : 100%
题目内容：
The mixture of his improved self-confidence and never-ending efforts is ________ lies behind his rapid progress in his study.
A. what B. that C. where D. which
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