Quadrilateral ABCD is a parallelogram. If adjacent angles are congruent, which statement must be true?

Step-by-step explanation:

A parallelogram is a shape that has two sets of parallel. There are a number of examples of parallelogram including but not limited to, square, rectangle, rhombus etc

From the question, the answer is, the shape is a rectangle. This is because the question says that the shape has its adjacent angles congruent, this means that they are supplementary(i.e they add up to 180). A rectangle is the one who fits the perfect description