Final answer:
Most letters, postcards, and invoices generated in a medical office are sent by postal mail.
Step-by-step explanation:
Most letters, postcards, and invoices generated in a medical office are sent by c. Postal mail. While email, fax, and courier service are also used for communication, postal mail is still widely used in medical offices for important documents and information. Postal mail provides a secure and tangible form of communication that is necessary for certain legal and confidential documents in the healthcare industry.