请基于题目内容生成一段5到10分钟讲解视频。要求：分析过程需按 “读题干雨图形结合→方法讲解→分步解题→得出答案→总结要点” 的顺序逐步推进，题目字体在不影响完整性的前提下尽量大。翻页尽量少，且不要有圈画动画，关键词用不同颜色字体表示，且确保逻辑清晰。---**Question Stem:**
如图, 图中有 _____ 个三角形, ∠B的对边是_____ .
(As shown in the figure, there are _____ triangles. The side opposite to ∠B is _____ .)
**Chart/Diagram Description:**
* **Type:** Geometric figure (triangle).
* **Main Elements:**
* **Points:** Three vertices labeled A, B, C. One point D is located on the line segment BC.
* **Lines/Segments:**
* Segment AB connects point A and point B.
* Segment AC connects point A and point C.
* Segment BC connects point B and point C.
* Segment AD connects point A and point D.
* **Shapes:** The figure contains three triangles:
* Triangle ABD
* Triangle ADC
* Triangle ABC