Earth's surface features are continually changing... this is due to a) wearing away of the surface

b) building up of the surface

c) both wearing away and building up

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.

the three components of a nucleotide are the nitrogenous base, the phosphate group and the five-carbon sugar.