The layer lining the lumen of the human alimentary canal is:

Options

A. Serosa
B. Sub-mucosa
C. Muscularis
D. Mucosa

Explanation

To answer the question "The layer lining the lumen of the human alimentary canal is:", we need to identify the correct layer from the options provided:

a) Serosa
b) Submucosa
c) Muscularis
d) Mucosa

### Step-by-Step Solution:

1. **Understanding the Structure of the Alimentary Canal**:
- The human alimentary canal is composed of four main layers from the innermost to the outermost: mucosa, submucosa, muscularis, and serosa.

2. **Identifying the Innermost Layer**:
- The innermost layer is the mucosa. This layer directly lines the lumen (the hollow part) of the alimentary canal.

3. **Reviewing the Other Layers**:
- **Serosa**: This is the outermost layer, made of mesothelium and connective tissue.
- **Muscularis**: This layer consists of smooth muscle, arranged in inner circular and outer longitudinal layers.
- **Submucosa**: This layer is made of loose connective tissue and contains blood vessels, nerves, and lymph vessels.

4. **Conclusion**:
- Since the question specifically asks for the layer that lines the lumen, the correct answer is the mucosa.

### Final Answer:
The layer lining the lumen of the human alimentary canal is **d) Mucosa**.