Geometry

Question Analysis：
This question describes a full figure reflection and asks for identifying the reflection line, using color-coded shapes.

Key Concept Explanation:
Reflection across y = x means swapping coordinates: (x, y) → (y, x)

Step-by-Step Solution：
Check point A(1, 0) → A′(0, 1) ✅
B(3, 2) → B′(2, 3) ✅
Others match too.

Option Analysis：
A. ✅ Correct — coordinate swap without sign change
B. Only flips y — not swap
C. Only flips x
D. Swap and sign flip — not what we see