ANSWER: use the ASA theorem
Step-by-step explanation:
Assuming parallelogram ABCD is shown where segment AB is parallel to segment DC and segment BC is parallel to segment AD.
According to the given information, segment AB is parallel to segment DC and segment BC is parallel to segment AD. Construct a diagonal from A to C with a straightedge. It is congruent to itself by the Reflexive Property of Equality. Angles BAC and DCA are congruent by the Alternate Interior Angles Theorem