讲解一下图中的这道题目---**Question Number:** 9 **Question Stem:** 已知线段 AB=5cm, 在直线 AB 上画点 C, 使 BC=1cm, 则线段 AC= ( )cm. **Options:** A. 6 B. 4 C. 6 或 4 D. 无法确定 **Chart/Diagram Description:** * Type: Line segment diagram. * Main Elements: * A horizontal line segment labeled with points A and B. * Point A is on the left end. * Point B is somewhere to the right of A. * A vertical mark indicates the position of A and B. * A label "5" with units "cm" is written above the segment AB, indicating its length. * Below the segment AB, there is another horizontal line with a point labeled "O". This seems unrelated to the main problem and might be from a different context or a stray mark. However, it's visible in the image. Let's focus on the segment AB part relevant to the question. * The question describes point C on the line AB, not necessarily between A and B. The diagram only shows the segment AB. The diagram does not show point C. **Other Relevant Text:** * Units: cm