Sentence arrangement: The sentence begins "The investigations of the ..." with labelled parts X: peculiar place in the economy of the body, Y: physiologist and the psychologist, Z: have revealed that the brain holds a. What is the most logical order of X, Y, and Z?

Introduction / Context:
This question examines your ability to arrange small fragments into a meaningful scientific sentence. The topic is investigations by specialists into the role of the brain in the human body. Correct ordering depends on both grammar and logical flow from investigators to their findings and then to the description of the brain's role.

Given Data / Assumptions:
- Beginning phrase: "The investigations of the ..." - X: "peculiar place in the economy of the body" - Y: "physiologist and the psychologist" - Z: "have revealed that the brain holds a" - We must form a coherent statement about investigations and the brain.

Concept / Approach:
First, we must complete the phrase "the investigations of the ..." by adding the people who conducted the investigations. Those people are "the physiologist and the psychologist", which is fragment Y. Next, a finite verb phrase should follow, and that is fragment Z, "have revealed that the brain holds a". Finally, the object of "holds" is given in X, describing the brain's "peculiar place in the economy of the body". This order respects both grammar and scientific sense.

Step-by-Step Solution:
Step 1: Attach the correct noun phrase after "the". The only phrase that can complete "the investigations of the" is "physiologist and the psychologist" (Y). Step 2: After naming the investigators, we need a verb. Fragment Z, "have revealed that the brain holds a", supplies the main verb phrase. Step 3: The verb "holds" requires an object. Fragment X, "peculiar place in the economy of the body", completes that object phrase. Step 4: The full sentence reads: "The investigations of the physiologist and the psychologist have revealed that the brain holds a peculiar place in the economy of the body." Step 5: This corresponds to the sequence Y Z X, which is option D.

Verification / Alternative check:
Try alternative orders to see why they fail. Starting with X would give "The investigations of the peculiar place in the economy of the body", which is illogical because we investigate things, not places "of the". Starting with Z or placing Z at the end would also break the sentence because every complete statement needs a main verb and object in the right order. Only Y Z X gives a clear subject "the investigations of the physiologist and the psychologist", a verb "have revealed", and a natural object describing the brain's special role.

Why Other Options Are Wrong:
Option A (Y X Z) tries to place the verb phrase at the end and leaves "have revealed that the brain holds a" without its full complement. Option B (X Z Y) produces a confusing subject and does not follow normal English syntax. Option C (X Y Z) similarly begins with an inappropriate phrase and fails to connect investigations with investigators properly.

Common Pitfalls:
Learners sometimes focus only on meaning without checking where the main verb must appear. A reliable method is to identify who did the action (investigations of which people), then locate the verb phrase, and finally add any objects or complements required. This approach simplifies many sentence arrangement questions in exams.

Final Answer:
The correct order is Y Z X, giving "The investigations of the physiologist and the psychologist have revealed that the brain holds a peculiar place in the economy of the body."