Geometry

Question Analysis：
This question tests precision in the definition of a glide reflection and what makes it unique.
The main focus is on the directional constraint of the translation relative to the mirror line.

Key Concept Explanation：
Glide reflection = reflection + translation parallel to mirror line
If translation is in any other direction, it is not a glide reflection
This directionality is what makes the glide reflection unique

Step-by-Step Solution：
Only one option correctly describes the essential condition for a glide reflection

Option Analysis：
A – ✖ Not always true; direction matters
B – ✖ Incorrect; translation must be parallel, not perpendicular
C – ✔ Corre...