What feature is most often used to define a state border when longitude and latitude are not used?

The sun's parallax would be 180 degrees, greater than which you can't get.  so a. would be your anwser 

The figure is not necessarily a parallelogram because only one diagonal is bisected and only one pair of sides is congruent.

Historians are researchers of the past or people who understand the history of people. with this field, they must possess qualities such as being unbiased, patient, efficient reader, has a knack for logic and critical thinking and reasoning, disciplined, open-minded, resourceful, with good analytical ability, good reasoning skills and problem solving!

B  maybe the answer hoped it