Why Are Monoclonal Antibodies So Useful

Why are monoclonal antibodies so useful?

A) They're easy to produce for any infection, so doctors can use them like medicines, and they only go after diseased cells.
B) They allow for a consistent supply of antibodies that target specific infections, so patients don't have to wait for just their own antibodies to build up, and they only go after diseased cells.
C) They are easy to produce and can target even cancer cells, but there are side effects on par with chemotherapy.
D) They're easy to produce for any infection, so doctors can use them like medicines, and they only go after diseased cells, but they don't last long so they constantly have to be remade.
E) They might be useful once they are approved for use in humans. So far the side effects are unknown.