A gradual change in the environment takes place slowly over a long period of time. Which of the following events usually changes the Earth's surface most gradually?

A. erosion
B. lightning
C. floods

in a chemical reaction, the atoms and molecules produced by the reaction are called products. no new atoms are created, and no atoms are destroyed. in a chemical reaction, reactants contact each other, bonds between atoms in the reactants are broken, and atoms rearrange and form new bonds to make the products.