Mainly to test you, line segments can measure length, rays and straight lines can't. Because we generally say that a straight road can be regarded as a straight line, it is easy for students to think that it is unmeasurable.

That's right, the road can be measured. This situation is wrong, such as the length of a straight line 10000 meters. Or straight lines are longer than rays, and so on. If you can't measure, you can't compare.