A eukaryotic organelle that can best be seen with the light microscope is the :

Options

A. endoplasmic reticulum
B. nucleus
C. polyribosome
D. microtubule

Explanation

To answer the question "A eukaryotic organelle that can best be seen with the light microscope is the:", we need to analyze the options provided: endoplasmic reticulum, nucleus, polyribosomes, and microtubules.

### Step-by-Step Solution:

1. **Understand the Options**:
- **Endoplasmic Reticulum (ER)**: This organelle is involved in protein and lipid synthesis. It is generally not visible under a light microscope due to its small size and the fact that it is often membrane-bound.
- **Nucleus**: This is the largest organelle in the cell, containing the cell's genetic material (DNA). It is typically large enough to be seen under a light microscope.
- **Polyribosomes**: These are clusters of ribosomes and are quite small, making them difficult to see with a light microscope.
- **Microtubules**: These are part of the cytoskeleton and are also too small to be seen clearly with a light microscope.

2. **Evaluate Visibility**:
- The nucleus stands out as the largest organelle among the options. Its size allows it to be easily observed under a light microscope, while the other organelles are either too small or not distinct enough to be seen clearly.

3. **Conclusion**:
- Based on the analysis, the organelle that can best be seen with a light microscope is the **nucleus**.

### Final Answer:
The correct answer is **nucleus**.