linear substitution

例句：

1. 1. The line of the road is straight and easy to follow.
   这条路线是直的，很容易跟随。
2. 2. The data is linearly related to the variable we are studying.
   数据与我们要研究的变量呈线性关系。
3. 3.The graph shows a linear increase in temperature with altitude.
   图表显示温度随海拔高度呈线性增加。