Geometry

Question Analysis：
This question tests your understanding of geometric transformations, particularly how a shape changes when reflected across the y-axis.
The main focus is identifying a y-axis reflection from a coordinate grid.

Key Concept Explanation:
A reflection across the y-axis flips each point horizontally over the y-axis:
(x, y) → (−x, y)
This means the shape appears mirrored on the opposite side of the vertical axis.

Step-by-Step Solution：
Observe the black triangle on the right of the y-axis.
The red triangle is the same size and shape, but placed symmetrically on the left.
Each point on the red triangle is directly across from the corresponding point on the black triangle, with x-values having opposite signs, but y-values the same.
This confirms a reflection across the y-axis.

Option Analysis：
A. ❌ Rotation changes orientation, but this shape is simply flipped.
B. ❌ X-axis reflection would flip the shape vertically (up/down), not horizontally.
C. ✅ Correct – this i...