Which of the following best defines 'selective toxicity' in antimicrobial therapy?

Any chemical that reduces the number of microbes on a surface regardless of effects on human cells

A drug that only targets viral pathogens because viruses are easiest to selectively target

A drug's ability to kill or inhibit a microorganism without causing unacceptable harm to the human host

A compound that indiscriminately kills both microbes and host cells to clear infection quickly