What two countries were most responsible for exploration and settlement of the plains regions

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!

Well, a and b together would be negative. b alone would also be negative.