Answer:
The correct answer is option c. free entry and exit.
Step-by-step explanation:
If a person has copyright or patent for a product others can not produce the same product without their permission. Copyrights and patents are barrier to entry and exit in a market and they restrict competition.
Similarly, government policies such as licencing, subsidies, tariffs on imports etc also reduce competition.
Free entry and exit allows firm to enter and leave the market thus it ensures competition.
So, option c is the correct answer.