帮我讲解一下这道题---**Question Number:** 31 **Question Stem:** In which triangle does the dotted line appear to be a line of symmetry? **Options:** A. A diagram showing a scalene triangle with a dotted line passing through one vertex and the opposite side. The dotted line does not divide the triangle into two congruent mirror images. B. A diagram showing an isosceles triangle with a dotted line passing through the apex vertex and the midpoint of the base. The dotted line appears to divide the triangle into two congruent mirror images, running vertically or slightly tilted vertically. C. A diagram showing a right-angled triangle with a dotted horizontal line passing through the triangle. The dotted line does not divide the triangle into two congruent mirror images. D. A diagram showing a scalene triangle with a dotted line passing through one vertex and intersecting the opposite side. The dotted line does not divide the triangle into two congruent mirror images. **Chart/Diagram Description:** The image contains four diagrams, labeled A, B, C, and D, each showing a triangle with a dotted line. - Diagram A shows a triangle. A dotted line is drawn from one vertex to intersect the opposite side. - Diagram B shows a triangle which appears to be isosceles. A dotted line is drawn from the top vertex to the base, appearing to bisect the base and potentially be perpendicular to it. This line looks like an axis of symmetry for an isosceles triangle. - Diagram C shows a right-angled triangle. A dotted horizontal line passes through the triangle, parallel to one of the legs. - Diagram D shows a triangle. A dotted line is drawn from a point on one side to a point on another side, approximately through the middle of the triangle. The dotted line in each diagram represents a potential line of symmetry for the triangle. A line of symmetry divides a shape into two identical halves that are mirror images of each other. Visually inspecting the diagrams, the dotted line in diagram B appears to be the only one that divides the triangle into two congruent mirror images.