Geometry

Question Analysis：
This question involves visual analysis of two overlapping triangles.
The main focus is on identifying the shared part (overlapping region) of the two shapes.

Key Concept Explanation:
When two triangles share a base (like BC), and the rest of their points (like A and D) are not in the same triangle, the only shared part is that common base.
We are not assuming the full triangles are the same — just overlapping at one edge.

Step-by-Step Solution：
Triangle ABC has vertices A, B, and C — it sits on top.
Triangle DBC has vertices D, B, and C — it sits below.
Both triangles share the same base: line segment BC
That’s the only part they have in common.

Option Analysis：
A. Only point B ❌ — B is shared, but so is C and the whole segment BC.
B. Only line segment BC ✅ — Correct! That’s the overlapping part.
C. Tr...