26. C. was
27. B. from
28. C. assistants
29. A. in
30. B. what

Rewritten sentences:
31. The first supermarket was opened in New York by a man named Michael Callen fifty years ago.
32. Supermarkets are different from other types of stores in several ways.
33. In supermarkets, goods are placed on open shelves, allowing customers to choose what they want and take them to the checkout counter.
34. The way products are displayed is another difference between supermarkets and many other types of stores.
35. Most customers go to a supermarket to buy goods from a shopping list, knowing exactly what they need to buy.