感觉这道题目选D说服力更强些，请NN指点。多谢。
Q29:
Over the past five years, the price gap between name-brand cereals and less expensive store-brand cereals has become so wide that consumers have been switching increasingly to store brands despite the name brands’ reputation for better quality. To attract these consumers back, several manufacturers of name-brand cereals plan to narrow the price gap between their cereals and store brands to less than what it was five years ago.
Which of the following, if true, most seriously calls into question the likelihood that the manufacturers’ plan will succeed in attracting back a large percentage of consumers who have switched to store brands?
There is no significant difference among manufacturers of name-brand cereals in the prices they charge for their products.
Consumers who have switched to store-brand cereals have generally been satisfied with the quality of those cereals.
Many consumers would never think of switching to store-brand cereals because they believe the name brand cereals to be of better quality.
Because of lower advertising costs, stores are able to offer their own brands of cereals at significantly lower prices than those charged for name-brand cereals.
Total annual sales of cereals—including both name-brand and store-brand cereals—have not increased significantly over the past five years. | 
