如图所示，直线a∥b，且△ABC的直角顶点A落在直线a上，点B落在直线a上，若∠1=16°，∠2=24°，则∠ABC的度数为（$\qquad$） A. 40° B. 45° C. 50° D. 55°---**Image Content Extraction:** **Geometric Diagram Description:** * **Type:** Geometric figure showing parallel lines and a triangle. * **Main Elements:** * Two parallel lines labeled 'a' (upper line) and 'b' (lower line). * Point A and Point C are located on line 'a'. * Point B is located on line 'b'. * A triangle ABC is formed by connecting points A, B, and C. The side AC lies on line 'a'. * **Angle Markings:** * Inside the triangle: Angle at vertex B (∠CBA) is marked with a single arc. Angle at vertex A (∠CAB) is marked with double arcs. Angle at vertex C (∠ACB) is marked with double arcs. * Outside the triangle: The alternate interior angle formed by the transversal line AB and the parallel line 'a' at point A is marked with a single arc. The alternate interior angle formed by the transversal line BC and the parallel line 'b' at point B is marked with double arcs. * **Perpendicular Lines:** Several perpendicular line segments are shown. Segments connecting line 'a' and line 'b' indicate the perpendicular distance between the parallel lines (height). There are also poorly drawn perpendicular symbols at points C (on line a, pointing away from a along AC) and B (on line b, pointing away from b along AB or CB). These perpendicular markings at C and B are geometrically inconsistent with C on line 'a' and B on line 'b' in this context and seem irrelevant to the angles shown. **Inferred Information and Relationships:** * Based on the angle markings inside the triangle: Let the angle marked with a single arc be 'x' and the angle marked with double arcs be 'y'. Then ∠CBA = x, ∠CAB = y, and ∠ACB = y. * This indicates that triangle ABC is an isosceles triangle with AB = BC (sides opposite equal angles are equal). * Based on the angle markings outside the triangle and the parallel lines 'a' and 'b': The alternate interior angle to ∠CBA (x) formed by transversal AB with line 'a' at A is marked as x. This is consistent with a || b. The alternate interior angle to ∠ACB (y) formed by transversal BC with line 'b' at B is marked as y. This is consistent with a || b. * **Mathematical Relationship:** The sum of the interior angles in triangle ABC is 180 degrees. Therefore: ∠CBA + ∠CAB + ∠ACB = 180° x + y + y = 180° x + 2y = 180°