Children in school are into different levels of grades，according to how much they know.A.

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A. bined
(答案→)B. classified
C. listed
D. clarified
解析：句意：根据孩子们知道的多少，他们在学校被分为不同层次的年级。classify意思为“将……分类，分班”；其他几个词没有这层意思，不合题意。bine结合；list列举，列出；clarify澄清，阐明。