Which property does a rhombus have?

A rhombus is a special type of parallelogram that has some distinct properties. One of the defining characteristics of a rhombus is that all four sides are of equal length, which means it has equal sides. Additionally, the opposite angles are equal, making option B the correct choice. This property of having both equal sides and equal opposite angles is what sets a rhombus apart from other quadrilaterals.

In contrast, the other options do not accurately describe the properties of a rhombus. For instance, the idea that only one pair of opposite sides is equal does not apply, as all sides must be equal. A rhombus does not require its angles to be right angles; in fact, the angles can vary while still maintaining the properties of a rhombus. Lastly, although the angles are equal in other shapes like a square, a rhombus does not have all angles equal unless it is also a square, which is a specific case of a rhombus. Therefore, option B correctly identifies the essential characteristics of a rhombus.