This Question Has Two Parts; Be Sure to Answer Both

This question has two parts; be sure to answer both.
First, distinguish among a hollow structure, a modular structure, and a virtual structure.
Second, specify whether each of the following companies has a hollow, modular, or virtual structure.
(a) Supreme Vacation Rentals, Inc., purchases every item that goes into its vacation rentals-from the furniture to the appliances and the bed linens-from suppliers all around the world. It then places all of these items into the vacation rentals before listing them for availability on the Internet.
(b) Fan Fiction publishes comic novels. It has only two people on staff who perform the company's core publishing functions: an editor who acquires the books from authors, and a marketer who serves as a publicist. All other functions, such as typesetting, printing, binding, warehousing, and distribution are outsourced to companies that can perform these services less expensively.
(c) Fly High is a small advertising agency. Its owner lives in Chicago, its account executive lives in Houston, its ad designer lives in Los Angeles, and its media buyer lives in Georgia. The four members of the Fly High team use Skype, Google Chats, and e-mail all day long to talk with one another and with their clients and prospective customers.