First, I am going to make an effort to simplify the principle in the stimulus. What is happening here? One skill is valued over another, and the author implies that this leads to adverse effects.
The convincing expert finds himself in a position of power despite lesser knowledge. Similarly, the politician who campaigns most effectively will succeed over the most knowledgeable.
What are the adverse effects? A less knowledgeable expert and a lack of insight into important political issues. This is why A is correct.
The problem with C is that we do not have an adverse effect. We know what the author believes is appropriate, but we do not know which opera singers are actually given the roles. C might be correct if it had said, "As a result, poor singers with good dramatic ability are being given most of the opera roles." Do you see how this element is missing from C, when it is present in the stimulus and answer choice A?
