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A. a plate of meat
B. a bowl of beef
C. a plate of chicken
答案:C
过点P(0,1)向圆x2+y2-4x-6y+12=0引切线,则切线长为______.
找正法装夹工件时,工件正确位置的获得是通过()达到的,夹具只起到()的作用。