Some bacteria cause diseases in humans and other organisms, but

O A. we don't know of any archaea that are harmful.

O B. viruses are unable to infect humans.

O C. antibiotics can always be used to treat bacterial infections.

O D. diseases caused by bacteria aren't serious.

The answer is C.

Explanation:

In bacterial viruses, antibiotics can be used to treat and eventually get rid of them, although in rare cases doctors and epidemiologists have been unable to find an antibiotic that can treat it, due to various reasons, but the majority of the time, in bacterial infections, antibiotics are the treatments doctors will want to use.

A. we don't know of any archaea that are harmful.

Explanation: Antibiotics can't always be used because the bacteria could get immune to it.-- - (Ur welcome! Mark brainlest! Future scientist here)