three & four

tri-
前缀含义：three; having three;
助记词：triangle;tri(three)+angle(角)→三角形
同缀词：triad,tricolour,tricycle,trident,trilogy,triple,tripod

stereo-
前缀含义：three-dimensional;
助记词：stereophonic;stereo（三维的）+phonic（声音）→三维的声音→立体声
同缀词：stereograph,stereotelevision,

音响和音乐设备上经常可以看到这个词

Stereophonic-–-Outputs-Inputs.jpg

quadr(i)-, quadru-
前缀含义：four;
助记词：quadruple;quadru（四）+ple（表倍数）→四倍的
同缀词：quadrennial,quadrilateral,quadrivalent,
quadrode,quadrumana,quadruped,