The contour interval is: a) the heavier contour lines with elevations printed on them b) the difference in elevation between two adjacent contours c) the rate at which the land elevation changes a coordinate system with perpendicular lines of uniform spacing

  b)  the difference in elevation between two adjacent contours

Explanation:

Each contour line corresponds to a particular elevation above some reference, usually sea level. The difference in elevations represented by adjacent contour lines is called the contour interval.

what events in mexico's history might explain why the country continues to have difficulty improving social justice and economic opportunities for all people?