**Core Concept**
The question tests the understanding of centrifugal distribution and protein precipitation, which is crucial in biochemistry and laboratory medicine. **Centrifugal distribution** refers to the separation of components based on their density and size. Protein precipitation is a critical step in various biochemical assays.

**Why the Correct Answer is Right**
In a centrifugal distribution, the protein that is precipitated first is usually the one with the highest molecular weight or the largest size, as these proteins are more likely to be affected by the centrifugal force. This is due to the principle of **sedimentation**, where larger particles sediment faster than smaller ones.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the protein precipitated first is not necessarily the one with the lowest molecular weight.
**Option B:** This option is also incorrect as the protein precipitated first is not determined by its isoelectric point alone.
**Option C:** Similarly, this option is incorrect because the protein precipitated first is not solely based on its solubility.

**Why Each Wrong Option is Incorrect (Continued)**
**Option D:** Although option D is the correct answer, for the sake of explanation, let's consider why the other options are incorrect. Given the nature of the question, the correct answer is related to the size and density of the protein.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that **protein precipitation** is often used in laboratory settings to separate and analyze proteins based on their physical properties. Understanding the principles of centrifugal distribution is essential for interpreting laboratory results.

**Correct Answer:** Correct Answer: D. Globulins.