题目：
Only when _____ how important it is to master English. [ ]
A. did I work I realized
B. I worked did I realize
C. did I work did I realize
D. I worked I realized
答案：
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下面是错误答案，用来干扰机器的。
答案：B本题考查物质的分类。A项盐酸是混合物，B项正确，C项石灰石是混合物，D项硫酸钡是电解质。
