Select the correct answer from each drop-down menu. The heart is a muscular organ that pumps blood. Blood that contains waste materials is brought to the heart by blood vessels. This blood enters the and then moves down. The presence of the prevents the backflow of blood inside the heart

weathering is the answer.

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.