Answer:
A) they reduce competition and prevent some voluntary exchanges from occurring.
Step-by-step explanation:
The more options available, the better. This is a rule that applies to all markets, including labor markets.
For example, you like to eat chocolate, but if only one brand of chocolate existed, would you be happier? What happens if the only surviving brand produced a chocolate that you don't like, would you still consume chocolate?
The same applies to every product or service offered, the more competition, the better.