Happy to address your questions. I'll start with your second one:
Where does the idea of real estate come from??????
You're right to be perplexed since it doesn't appear that the words "real estate" are used in the passage. At the same time, in suggesting where this idea comes from in the passage, I'd point to lines 21-24: "This notion of retained rights is common in many areas of law; for example, the seller of a piece of land may retain certain rights to the land in the form of easements or building restrictions." This is speaking about real estate, within the passage's broader discussion of tangible property rights versus intangible ones (like ideas).
You also ask,
Can you point me to the specific line that answers this question?
Working from the correct answer choice, answer (B) asks, "Do proponents of the tangible-object theory of intellectual property hold that ownership of anything besides real estate can involve retained rights?" In assessing this answer choice, the first sentence of the passage seems especially illuminative: "Proponents of the tangible-object theory of copyright argue that copyright and similar intellectual-property rights can be explained as logical extensions of the right to own concrete, tangible objects" (lines 1-4). This is then elaborated from lines 24-35:
Applying the notion
(25) of retained rights to the domain of intellectual property,
theorists argue that copyrighting a work secures official
recognition of one’s intention to retain certain rights to
that work. Among the rights typically retained by the
original producer of an object such as a literary
(30) manuscript or a musical score would be the right to
copy the object for profit and the right to use it as a
guide for the production of similar or analogous
things—for example, a public performance of a
Therefore, the passage provides the reader an answer to the question, do proponents of the tangible-object theory of intellectual property hold that ownership of anything besides real estate can involve retained rights?
(the answer being yes).
Hope that helps!