Concept:Soil formation depends on both passive and active factors; climate is the main active factor.
Explanation:Active factors directly supply energy and materials that drive soil-forming processes.
Climate controls rainfall and temperature, which influence weathering rate, decomposition of organic matter, and leaching.
Relief and slope are passive topographic factors that only modify drainage and erosion.
Time is also a passive factor because it simply allows processes to act over a duration.
Thus, among the given options, climate is the most important active factor.
Answer:D. climate