The nurse is explaining antibiotics classification with a nursing student. It would be correct if the nurse included which statement?

a. Narrow spectrum antibiotics usually are effective against one type of organisms.
b. Narrow spectrum antibiotics are used to treat infections when the microorganism has not been identified.
c. Broad spectrum antibiotics are selective and only treat one type of infection.
d. Broad spectrum antibiotics are either effective against gram negative or gram positive microorganisms, not both.