Official Explanation
For an assumption, we can use the Negation Test. The credited answer is (C). If prosperity and ownership of property & assets are not essentially related, then folks with higher education could have the property & assets but not have prosperity. Negating this statement jeopardizes the argument, so this statement is an assumption of the argument.
Those skills may always be covered in college education, but perhaps folks can also develop those skills on their own, without a college education, and thus be capable of performing well in such a job, earning the high salary, and achieving prosperity --- all without a college education. This allows for an exception, so this is not a valid assumption. Choice (A) is incorrect.
Initially, choice (B) sound reasonably, but it's certainly possible that some rich person owns real estate as investments and, because of lifestyle, rents luxury apartments in two or three cities, rather than living in a house that she owns. This does not necessarily support the argument, so choice (B) is incorrect.
Understanding what prosperity is does not automatically result in achieving it, any more than understanding how digestion works might relieve really feelings of hunger! Choice (D) is incorrect.
Choice (E) is too extreme. The argument is making the case that one needs a college degree to get to the level of full prosperity --- real estate and long term assets. It's possible that someone in a lower paying job is part of the way there --- maybe owns a few stocks, or has no investments but owns a relatively inexpensive house. We can't make a clear yes-vs.-no distinction, total prosperity vs. absolutely no prosperity. That's too extreme. Choice (E) is incorrect.