Which polygon has opposite sides equal and parallel to each other and all its angles measure 90°?

A parallelogram is a quadrilateral whose opposite sides are parallel and equal. The opposite angles of a parallelogram are also equal.

A rhombus is a parallelogram in which all sides are equal.
A square is a unique kind of rhombus with opposite sides equal and parallel to each other and all its angles measure 90°.
Therefore, option B is the correct answer.