Step 1: Check the square. A square has 4 lines of symmetry: (i) Vertical line through midpoints of top and bottom sides (ii) Horizontal line through midpoints of left and right sides (iii) Diagonal from top-left to bottom-right (iv) Diagonal from top-right to bottom-left Total = 4 lines of symmetry. Step 2: Check the other options. Rectangle (length ≠ width): 2 lines only (through midpoints; diagonals do not work). Equilateral triangle: 3 lines (one from each vertex to the opposite midpoint). Rhombus (non-square): 2 lines (the two diagonals only). Answer: Square