Which of the following is not a broad-spectrum antibiotic?

Penicillin (specifically Penicillin G) is a narrow-spectrum antibiotic because it is effective primarily against a limited range of Gram-positive bacteria. Tetracycline and Chloromycetin (Chloramphenicol) are broad-spectrum antibiotics as they act against a wide range of both Gram-positive and Gram-negative bacteria.