IMO

A. There is no significant difference among manufacturers of name-brand cereals in the prices they charge for their products. - This info is useless for us. Knowing this we can't answer to the question: "Will the plan succeed?"

B. Consumers who have switched to store-brand cereals have generally been satisfied with the quality of those cereals. - Yes! This helps us! If we know that consumers which switched to store-brand cereals like that cerals for the quality, they really don't care too much about the price. So making cheaper the name-brnad cereals, it won't increase their sales.

C. Many consumers would never think of switching to store-brand cereals because they believe the name brand cereals to be of better quality. - This is just the opposite of what is said in the question stem. Consumers switched to store-brand cereals.

D. 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. - Yes, but the question says that name-brand cereals will narrow this gap...you have to find an answer choice that introduces some new info..this answer is just repeating the question stem

E .Total annual sales of cereals-including both name-brand and store-brand cereals-have not increased significantly over the past five years. - This is out of scope. We don't care about annual sales. We care about attracting back consumers by implementing a plan (in the future)