Which figure must be a square?

A.

a quadrilateral with four right angles

B.

a rhombus with four right angles

C.

a parallelogram with four congruent sides

D.

a quadrilateral with congruent sides

B is correct because by default a rhombus has four equal sides, and it says it also has four right angles. A is incorrect because it could refer to any rectangle, C is incorrect because parallelograms don't necessarily have four right angles, and D is incorrect because quadrilaterals don't necessarily have four right angles either.