Some bacteria cause diseases in humans and other organisms, but

A. Antibiotics can always be used to treat bacterial infections.

B. We don't know of any archaea that are harmful.

C. Viruses are unable to infect humans.

D. Diseases caused by bacteria aren't serious.

A) Antibiotics can always be used to treat bacterial infections.

The right option right here is option A. Antibiotics can always be used to treat bacterial infections.

What happens here is, the use of antibiotics started with Alexander Fleming, a scientist who discovered penicillin, an antibiotic so strong that it could cure a lot of bacterial diseases during that time. But what he didn't know is that bacterias can adapt themselves, developing in this way a protection against this antibiotic, that's why nowadays we have superbacteria, this kind has lots of protections in its genes that we can't almost fight them with our medicine. Some antibiotics do a very good job at destroying bacterial cell wall, thats how some of them work.