As far as I know, the positive and lively activities ________ our students, who used to focus on just remembering knowledge, to use their knowledge freely．
A.motivate
B.motivated
C.have motivated
D.had motivated
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C解析考查时态。通过句子的语境as far as I know可知，动作与现在有关，排除B、D两项，且motivate这个动作到现在为止已发生了，故用完成时。