In right Fig.,if the length of the segment AB is 1,M is the midpoint of the segment AB,and point C divides the segment MB into two parts such that MC:CB=1:2,then the length of AC is {#blank#}1{#/blank#}。 (英汉词典:length 长度;segment 线段;midpoint 中点;divides…into 分为,分成)