The proof shows that abcd is a rectangle. which of the following is the missing reason ?

The correct answer is: Opposite angles of a parallelogram are congruent.

In a parallelogram, the opposite angles are always congruent. The opposite angles are the angles diagonal across from each other.

You can tell by the order of ABCD that A and C are opposite. B and D are also opposite of each other and congruent.

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