如图,在▱ABCD中,BM是∠ABC的平分线交CD于点M,且MC=2,▱ABCD的周长是14,则DM等于( )
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课外活动小组的同学想要估测同学在做引体向上时的功率.下列中不用测量的物理量是( )
——Jack , you look tired today. What’s wrong?——I was ____busy_______ I didn't go to bed until midnight yesterday.