Question

which step in the construction of copying a line segment ensures that the new line segment has the same length as the original line segment?

Answer 1

like a first step how you constract a line segment ?

Answer 2

Here are the steps for copying a line segment: https://www.mathopenref.com/printcopysegment.html

We are looking for which step helps to keep the new copy of the line segment the same length as the original one. We're looking for something like "equal" (in that link) because we want "equal" length.