Hi,
So the correct answer would be B, Indonesia. If we look at a map of the world, we can see that Chile, Romania and Turkey are countries which are in contact with a major land mass, meaning more contact with other people and countries.
Indonesia, on the other hand, is made up of multiple islands, meaning that it is harder for diseases to be spread throughout the whole country, as it will have to travel from island to island in order to have great impact on the whole country.
-Hope this helps!