Final answer:
Trimethoprim/sulfamethoxazole is the appropriate first-line antibiotic choice for a 16-year-old girl with a simple urinary tract infection, and azithromycin would not be a typical choice for a UTI.
Step-by-step explanation:
The first-line antibiotic choice for a 16-year-old female with a urinary tract infection (UTI) who is otherwise healthy and has no recent antibiotic use would likely be trimethoprim/sulfamethoxazole (B). This combination therapy is often used for uncomplicated UTIs and is effective against the common causative agents such as E. coli. Other options like azithromycin are not typically used for UTIs, except in specific cases such as certain sexually transmitted infections. Ceftriaxone is a broad-spectrum antibiotic that may be used for more complicated UTIs or pyelonephritis. Levofloxacin, a fluoroquinolone, is generally reserved for cases where other treatments have failed or are not suitable, due to concerns about resistance and side effects.