1. The problem asks: "All ............... are similar." with options (a) triangles, (b) rectangles, (c) parallelograms, (d) squares. 2. Similar figures have the same shape but not necessarily the same size. They have equal corresponding angles and proportional corresponding sides. 3. Among the options: - Triangles can be similar if their corresponding angles are equal and sides are proportional, but not all triangles are similar. - Rectangles have all angles equal (90 degrees), but their sides can vary, so not all rectangles are similar. - Parallelograms have equal opposite angles and sides, but not all parallelograms are similar. - Squares have all sides equal and all angles 90 degrees, so all squares are similar to each other. 4. Therefore, the correct answer is (d) squares. Final answer: All squares are similar.