Why are genetically engineered mammalian cells sometimes needed to produce certain proteins instead of genetically engineered bacteria? A. Mammalian cells are not needed; bacterial cells can produce the same proteins as long as they have the gene that codes for it. B. Mammal cells have more precise restriction enzymes. C. Mammal cells are larger and can produce greater volumes of protein. D. Bacteria make proteins differently than mammals, and cannot make certain human proteins.