问题
选择题
—What about the student in your class, Mr. Wang?
—The doctor said that ________ sleep caused him poor memory and poor concentration.[ ]
A. lacking of
B. lacked in
C. lacking
D. lack for
答案
答案：C
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学生关系student的主码是sno，课程关系course的主码是cno，选课关系sc的主码是(sno，cno)。
