An auto-immune disease is

Options

A. (a) SCID
B. (b) rheumatoid arthritis
C. (c) myasthenia gravis
D. (d) all of the above

Explanation

### Step-by-Step Solution:

1. **Understanding Autoimmune Diseases**:
- Autoimmune diseases occur when the immune system mistakenly attacks and damages the body's own tissues. This happens due to the immune system's inability to differentiate between self (the body's own cells) and non-self (foreign cells).

2. **Analyzing the Options**:
- **A. SCID (Severe Combined Immunodeficiency)**:
- This is primarily an immunodeficiency disorder where the body cannot fight infections effectively. While it has autoimmune components, it is not classified primarily as an autoimmune disease.
- **B. Rheumatoid Arthritis**:
- This is a chronic inflammatory autoimmune disease where the immune system attacks the joints, leading to pain and inflammation.
- **C. Myasthenia Gravis**:
- This is a neuromuscular autoimmune disease where antibodies attack the nerves that stimulate muscles, leading to muscle weakness.

3. **Conclusion**:
- Since both Rheumatoid Arthritis and Myasthenia Gravis are classified as autoimmune diseases, and SCID has autoimmune aspects but is mainly an immunodeficiency disorder, the best answer here is **D. All of the above**. This is because all three options involve aspects of the immune system malfunctioning.

### Final Answer:
**D. All of the above**