Help plz... what are the missing proof
A. Substitution; converse of diagonals theorem
B. Sum of interior angles; converse of opposite angles theorem
C. Substitution, converse of opposite angles theorem
D. Sum of interior angles; converse of diagonals theorem
I think it's between B and C ​

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."