The world's finest single-malt whiskies come from the highland of

The conclusion is

MacDuff's whisky must be the finest whisky in the world

(A) The more single-malt whiskies involved in the batch of blended whisky, the finer the quality of whisky.
--Strengthens the conclusion
--Out

(B) Whereas many of MacDuff's competitors have been in industry for decades or even century, the MacDuff brand was created within the last decade by marketing committee.
--Has nothing to do with single malt and blending
--Out

(C) Including more than five single-malt whiskies in a blended whisky is a waste, because no one can taste that many component flavors.
---right , but no fewer than five Scotland's finest single-malt means >=5
it means the blended malt can have 5 single malt whiskies
--Out

(D) A blended whisky is as fine as the average quality of its components.
---This means that either the blended one's quality is same or inferior
if all say 10 ingredients have a value of 10 , the value of blended whiskey will be 10
if any one of the ingredient has a lower value the average will go down .
--Should be the answer

(E) The concept of "finest" in a whisky is a subjective measure that cannot be quantified in a statistically valid way
--May be true , but it doesn't weaken the conclusion
--Out

D !!