Amazon is dominant in online book retailing, and Wayfair is dominant in online furniture retailing. What cost conditions is consistent with this market structure?

The concentration of almost all online retail book sales to just one firm, Amazon, is most consistent with market structure exhibiting (diseconomies or scale/economies of scale/neither). Setting up book-specific retailers would be (less efficient than/just as efficient as/ more efficient than) retailing all books in one firm.

The online pre-prepared meals segment includes competitors Blue Apron, Cornershop, Instacart, Fresh Direct, Hello Fresh, and Shipt. What cost condition is consistent with this market structure?

Due to the (similarities/differences) in the shipping, storage, and distribution of groceries versus ingredients packaged as kits, if Instacart or Blue Apron decided to produce both, then they would have to create two different processes to ship, store, and distribute the goods as well as take on the costs associated with the two processes. The pre-pared meal market exhibits (economies of scope/ diseconomies of scope). In this case, separating the pre-prepared meal market into grocery delivery and kit delivery is (less efficient than/just as efficient as/ more efficient than) consolidating.