The author is considering adding this sidebar to the passage:

A veterinarian, "vet" for short, is a type of physician who provides medical treatment to animals. Many veterinarians specialize in a specific field such as companion animal (or pet) medicine, which focuses on animals such as cats and dogs, or equine medicine, which focuses on horses. Other vets may choose to specialize in caring for livestock, reptiles, birds, or other animals. In addition to a traditional four-year undergraduate degree, veterinarians must attend four years of veterinary school, which includes at least one year of hands-on training in clinical rotations. Veterinarians earn a broad range of salaries, but those who own their own practices typically earn the most.
How would this sidebar support the information in the passage?
A) It describes what the narrator would have to do to become a veterinarian.
B) It explains why veterinarians need as much training as doctors for humans.
C) It provides a comparison of the salaries of different veterinary specialties.
D) It illustrates why many veterinarians choose to specialize in a certain field.