请帮我讲一下这道题---**Extraction Content:** **Question Stem:** 5. 如图, DE 是 △ ABC 的中位线, ∠ABC 的角平分线交 DE 于点 F, AB = 6, BC = 9, 则 EF 的长为 **Options:** A. 0.5 B. 1 C. 1.5 D. 2 **Chart/Diagram Description:** * **Type:** Geometric figure (triangle). * **Main Elements:** * **Points:** Labeled points A, B, C forming a triangle. Point D is on side AB, and point E is on side AC. Point F is located on the line segment DE and also on a line segment originating from B. * **Lines/Segments:** * Triangle ABC is formed by segments AB, BC, and AC. * Segment DE connects point D on AB to point E on AC. Segment DE is drawn as a horizontal line across the triangle, appearing roughly parallel to BC. * Segment BF is drawn from vertex B and intersects segment DE at point F. * **Labels:** Points are labeled A, B, C, D, E, F. **Interpretation based on text:** * DE is the midsegment of triangle ABC. This means D is the midpoint of AB and E is the midpoint of AC. It also implies DE is parallel to BC and DE = 1/2 * BC. * BF is the angle bisector of angle ABC. This means BF divides angle ABC into two equal angles. * F is the intersection point of the angle bisector BF and the midsegment DE. * Given lengths: AB = 6, BC = 9.