Animal cells have all of the following except
a. mitochondria.
b. chloroplasts.
c. a nucleus.
d. golgi apparatus.

Animal cells do not have chloroplasts, so answer choice (B) is the correct one. All animals (unless there are any bizarre exceptions that I'm not aware of, or as long as we're not categorizing some unicellular organisms as animals) are eukaryotic, which means that their cells contain nuclei, meaning that (C) is not valid. Mitochondria are found in all eukaryotic cells, including those of mammals, so (A) is also not correct. The Golgi apparatus is another organelle found in eukaryotic cells, and they are found in animal cells, so (D) is not correct. But chloroplasts are the organelles responsible for conducting photosynthesis, which is something that only plants and not animals are capable of, so there are no chloroplasts in animal cells.