The teacher, ________ that his students have difficulty in English grammar, has decided to give them some further drilling．A.knowingB.knownC.to knowD.being known
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A解析难。考查非谓语动词。本句的主句是The teacher has decided to give them some further drilling．中间的结构应该是一个可充当状语的分词结构，表示“当老师知道他的学生在学语法上有困难时……”，是主动形式，故用knowing。