The of a surface determines the amount of stress on earth materials such as soils and rocks.

I think you forgot to mention the options along with the question. I am answering the question based on my research and knowledge. The vegetation of a surface determines the amount of stress on earth materials such as soils and rocks. I hope it helps you. 

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So  if  the sum of the enthalpies of the reactants is greater than the products, the  reaction  will be  exothermic.  if  the products side has a larger enthalpy, the  reaction  is  endothermic. you may wonder why  endothermic reactions, which soak up energy or enthalpy from the environment, even happen