The correct options are
Narrow spectrum antibiotics are used against only limited pathogens. Penicillin, gentamycin and erythromycin are used to treat only certain pathogens such as Staphylococci, Clostridia, Streptococci and hence fall under the class of narrow spectrum antibiotics. They are usually used when the pathogen is known. Broad spectrum antibiotics are used when the symptoms of a disease are visible but the pathogen is unknown.