Which of the following best translates "Call an ambulance" into Spanish?

The phrase "Call an ambulance" translates to Spanish as "Llama a una ambulancia." This translation directly conveys the request to contact emergency medical services. The verb "llama" means "call," and "una ambulancia" clearly indicates the specific service required.

To provide context for the other options, "Llame a la policía" means "Call the police," which is not relevant to requesting an ambulance. "Llama a un médico" translates to "Call a doctor," which also does not specifically address the need for transportation to a medical facility. "Llame a un amigo" means "Call a friend," which similarly does not pertain to the request for emergency services. Thus, the choice that accurately reflects the intended action is to call an ambulance, making this the correct translation.