No doctor is a quack. Some quacks are consultants. Which of the following conclusions is valid?
Correct: B
The middle term 'quacks' is distributed in the first premise (No D are Q) but undistributed in the second premise (Some Q are C). This is the fallacy of the undistributed middle. No valid conclusion linking doctors and consultants can be drawn. The syllogism is invalid. None of the given conclusions follows necessarily.