Many brick-and-mortar bookstores are in poor operating conditions and even difficult to maintain, while a large number of online bookstores are selling hotly. Some people have analyzed that this is mainly because online bookstores are cheaper than physical bookstores, so they are more competitive. What are the assumptions implicit in this person's analysis? ['Price is the main consideration for consumers when buying books.', 'The online bookstore provides home delivery service.', 'Online and physical bookstores have the same quality.', 'Price is the main competitive factor in sales.']