Step 1: Understanding the Concept:
This question asks us to identify the distinction the author makes between studying phobias/obsessions and studying dreams. We need to find the word that describes the former but not the latter, according to the first paragraph.
Step 2: Detailed Explanation:
Let's look at the relevant sentences in the first paragraph:
- "...the hysterical phobia, the obsession, and the delusion—must interest the physician for practical reasons."
- "The dream can lay no claim to a corresponding practical significance; however, its theoretical value is very great..."
The author explicitly states that phobias, obsessions, and delusions have "practical reasons" for study, while dreams have no "practical significance." Therefore, the distinguishing quality is being "practical."
Step 3: Final Answer:
The text directly contrasts the "practical" nature of studying phobias with the non-practical (but theoretical) nature of studying dreams. Option (C) correctly fills in the blank.