26. [E] challenges
27. [J] searched
28. [D] categorizing
29. [K] similarities
30. [L] slightly
31. [G] percentage
32. [O] traditional
33. [ I ] regardless
34. [H] proving
35. [M] suggests
46. [B] He intends to get rid of the tipping practice.
47. [C] It forces the customer to comensate the waiter.
48. [D] They can have some say in how much their servers earn.
49. [A] Services quality has little effect on tip size.
50. [D] Waiters should be paid by employers instead of customers.
51. [C] The impact of cheap oil on global economic growth.
52. [D] Consumers will spend their savings from cheap oil on other commodities.
53. [C] They use their money reserves to back up consumption.
54. [B] Its negative effects more than cancel out its positive effects.
55. [A] People are not spending all the money they save on gas.