Each program brings together different subjects and extends in length over two or three quarters.

VOA: special.2009.03.05

There are some questions that might be a different length.

还有些问题,可能长度不同。

麻省理工公开课 - 固态化学导论课程节选

At each point, er is a different vector pointing in the radial direction of length one.

矢量 er 在每一点处都不同,方向都从圆心指向该点,模长为1

耶鲁公开课 - 基础物理课程节选