**Core Concept:** In a light microscope, the arrangement of lenses plays a crucial role in the focusing and magnification of the image being viewed. Light enters the microscope through the objective lens, which is the primary lens, and then passes through the ocular lens, which is the secondary lens. The combination of these two lenses is essential for forming a clear and magnified image of the specimen.

**Why the Correct Answer is Right:**

The correct answer, **Correct Answer: D**, refers to the correct arrangement of lenses in a light microscope:

1. **Option A (missing secondary lens):** This option does not include the ocular lens, which is necessary for magnification and image viewing. A light microscope requires both objective and ocular lenses for proper functioning.
2. **Option B (improper arrangement of lenses):** The lenses could be arranged in an incorrect way, leading to a distorted or unclear image. The correct arrangement ensures that the image is formed and magnified correctly.
3. **Option C (missing primary lens):** A light microscope relies on the primary objective lens to focus and magnify the specimen. Without this lens, the microscope cannot function as intended.
4. **Option D (correct arrangement of lenses):** This option accurately represents the arrangement of lenses in a light microscope. The primary objective lens focuses the light, and the secondary ocular lens magnifies the focused image, resulting in a clear and magnified view of the specimen.

**Why Each Wrong Option is Incorrect:**

- Option A lacks the essential ocular lens.
- Option B has an incorrect arrangement of lenses, leading to an inaccurate image.
- Option C misses the primary objective lens, preventing the microscope from functioning properly.

**Clinical Pearl:**

Understanding the correct arrangement of lenses in a light microscope is crucial for obtaining a clear and magnified view of the specimen. Proper use of a light microscope is essential for medical students, pathologists, and researchers to study microorganisms, cells, and other small structures accurately.