Answer:
B. Sum of interior angles; converse of opposite angles theorem
Step-by-step explanation:
In statement 1, all the interior angles of the quadrilateral are added to give a sum of 360°. The reason would therefore be "sum of interior angles".
As a follow up to the already established fact that the opposite angles of the quadrilateral are congruent to each other, this satisfies the Converse of Opposite Angles Theorem, which states that if the opposite angles of a quadrilateral are congruent to each other then the quadrilateral must be a parallelogram.
Reason for the statement in number 6 is definitely "converse of opposite angles theorem."
