Why is an index contour different from other contour lines?   a. it indicates a greater change in elevation.   b. it is drawn more darkly on a topographic map.   c. it signifies where elevation begins to decrease.   d. it shows the elevation from which other points are measured.

Who ever answer first get ! question 1 : which pair of words names two processes for treating water to make it clean? a. aeration, precipitation b. coagulation, refurbishing c. filtration, coagulation d. combustion, aeration question 2: which act did the u.s congress pass in 1972 to protect th nation's water? a. anti-pollution act b. watershed protection act c. clean water act d. nixon act