1. **Problem:** Determine which quadrilateral always has equal diagonals. 2. **Understanding the problem:** We are given four types of quadrilaterals: parallelogram, rhombus, rectangle, and trapezium. We need to identify which one always has diagonals of equal length. 3. **Recall properties:** - Parallelogram: Opposite sides are equal and parallel, but diagonals are generally not equal. - Rhombus: All sides equal, diagonals are perpendicular but not necessarily equal. - Rectangle: Opposite sides equal and all angles 90°, diagonals are equal. - Trapezium: Only one pair of opposite sides parallel, diagonals are generally not equal. 4. **Conclusion:** The quadrilateral with always equal diagonals is the **rectangle**. **Final answer:** (c) rectangle