relationship, established equivalent relationship 14, and subject: applicatiproblem (4)--scores and percentage application problem review content overview answers scores, and percentage application problem of key is: accorning, (1) determine standard volume (units \hen in-line solution. Category fraction multiplication word problem score Division applications engineering problem problem XV, a subject: review of the meapacity, measurement and units of measurement of common units of measurement and their significance in rate 1, currency, leth, area, volume, unit sizegeometry preliminary knowledge (1)--line and angle review content line, aon nd segment, and Ray, and vertical, and parallel, and angle angle of classification (slightly) 17, and subject: geometry preliminary knowledge (2)--plane grading to meaphics review content triangle, and edges shaped, and round, and fan axisymmetric graphics perimeter and area combination graphics of area subject : Preliminary knowledge (3)-review of solid content category 1-d shapes are divided into: cylinder and cone 2, column is divided intsurement o: cuboid, of the amount of casquare 3, cone cone of the features of cuboids and cubes relationship between characteristics of circular cone is slightly solid surface area and volngume 1, size 2, table ...和, volume, weight and rate. (Omitted) 2, commonly used time units and their relationships. (Slightly) with a measurement units Zhijian of of poly 1, and of method 2, and poly method 3, and of method and poly method of relationship measurement distance of method 1, and tool measurement 2, and estimates 16, and subject: 文献综述
一． 绪论
1. 交通灯的由来：
交通灯是指由红、黄、绿三种颜色灯组成用来指挥交通的信号灯，最早出现在19世纪初在英国中部的约克城的一个典故中，当时交通灯只有两种颜色红绿，随着各种交通工具的发展和交通指挥的需要，第一盏名副其实的三色灯(红、黄、绿三种标志)于1918年诞生。它是三色