An autoimmune disease is:

Options

A. AIDS
B. haemophilia
C. allergy
D. myasthena gravis

Answer

### Step-by-Step Solution:

1. **Understanding Autoimmune Diseases**:
- Autoimmune diseases occur when the immune system mistakenly attacks the body's own healthy cells. This happens due to a malfunction in the immune response, which is typically designed to protect the body from foreign invaders like viruses and bacteria.

2. **Analyzing the Options**:
- The question provides four options: AIDS, hemophilia, allergy, and myasthenia gravis. We need to determine which of these is classified as an autoimmune disease.

3. **Evaluating Each Option**:
- **AIDS**: This disease is caused by the Human Immunodeficiency Virus (HIV) and is not an autoimmune disease. It primarily affects the immune system but does not involve the immune system attacking the body’s own cells.
- **Hemophilia**: This is a genetic disorder that affects blood clotting due to the absence of certain clotting factors. It is not an autoimmune disease.
- **Allergy**: Allergies are immune responses to foreign substances (allergens) and do not involve the immune system attacking the body’s own cells. Therefore, this is also not an autoimmune disease.
- **Myasthenia Gravis**: This condition is characterized by weakness in the skeletal muscles and is caused by antibodies produced by the immune system that block the receptors for acetylcholine, a neurotransmitter essential for muscle contraction. This is a classic example of an autoimmune disease.

4. **Conclusion**:
- After evaluating all the options, the only condition that fits the definition of an autoimmune disease is **Myasthenia Gravis**.

### Final Answer:
**Myasthenia Gravis** is an autoimmune disease.

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