I'm going with D...

The advertisement states that Northwoods Maple Syrup is made the old-fashioned way and it is "simply tops for taste". As evidence the advertisement presents a survey in which 7 out of every 10 shoppers who expressed a preference said that Northwoods was the only maple syrup for them.

Question Stem: Of the following, which one is the strongest reason why the advertisement is potentially misleading?

(A) "The proportion of shoppers expressing no preference might have been very small". Incorrect. The survey is of shoppers who expressed a preference. This answer implies that the proportion of shoppers expressing a preference is large. This strengthens the advertisement as it means that there was a large population from which to draw a sample for the survey.

(B) "Other brands of maple syrup might also be made the old-fashioned way". Incorrect. The advertisement claims that 7 out of 10 people prefer Northwoods syrup. They are comparing Northwoods to all other choices. The fact that other syrups may also be made the old-fashioned way is irrelevant.

(C) "No market survey covers more than a sizable minority of the total population of consumers". Incorrect. This answer implies that the survey sample was small. This does not necessarily mean that the survey is misleading. As long as the sample is representative of the greater population it is valid.

(D) "The preference for the Northwoods brand might be based on such a factor as an exceptionally low price". Correct. The advertisement claims that Northwoods maple syrup tastes great. As evidence they provide the survey showing a strong preference for their brand. This answer suggest that the preference might be based on other factors such as an exceptionally low price. If this is true then the advertisement's claim the syrup's taste is superior is misleading.

(E) "Shoppers who buy syrup might buy only maple syrup". Incorrect. The advertisement states that people prefer Northwoods maple syrup to all other maple syrup choices. The fact that shoppers buy only maple syrup does not damage their claim.