The condition of non-exclusiveness means that: It is difficult to keep someone from benefiting from a public good.; There are negative externalities associated with a public good.; The public good is not very fancy.; or There are positive externalities associated with a public good.

I think it is There are negative externailities associated with a public good.

I disagree with your answer.

Non-exclusiveness means that everyone can be part of the program.

Actually, the correct answer is "It is difficult to keep someone from benefiting from a public good." The condition of non-exclusiveness refers to the fact that, once a public good is provided, it is not possible to exclude anyone from enjoying its benefits. In other words, individuals cannot be prevented from benefiting from a public good, regardless of whether or not they contribute to its provision.

To arrive at this answer, you can eliminate the other options through the process of elimination:

1. "There are negative externalities associated with a public good" is incorrect because non-exclusiveness does not necessarily imply negative externalities. Negative externalities refer to the costs imposed on third parties due to the production or consumption of a good. Public goods can have positive externalities.

2. "The public good is not very fancy" is incorrect because the condition of non-exclusiveness has nothing to do with the quality or fancy nature of a public good. It is solely about the difficulty of excluding individuals from benefiting.

3. "There are positive externalities associated with a public good" is incorrect for the same reasons mentioned above. Non-exclusiveness does not imply positive externalities, although public goods can have positive externalities.

So, the correct answer is indeed "It is difficult to keep someone from benefiting from a public good."