Scientists believe that ancient ancestors of all animals were.
a. single-celled prokaryotes that reproduced asexually
b. single-celled eukaryotes that sometimes grew in colonies
c. multi-cellular organisms that were probably autotrophic.
d. multi-cellular organisms with an alternation of generations lifecycle.

The correct answer is B. Single-celled prokaryotes that sometimes grew in colonies

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.