--- I found your foreign friends didn’t laugh a lot over my jokes. ---Don’t be silly. You know culture differences? Being a foreigner, he didn’t ____these jokes. A. catch on B. get on C. focus on D. take on 答案:A
如图,在棱长为2的正方体ABCD-A1B1C1D1中,O是底面ABCD的中心,E、F分别是CC1、AD的中点.那么异面直线OE和FD1所成的角的余弦值等于
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