**Core Concept**
Mysthenia gravis is an autoimmune disease characterized by the production of antibodies against the acetylcholine receptor (AChR) at the neuromuscular junction. This leads to impaired neurotransmission and muscle weakness.

**Why the Correct Answer is Right**
The correct answer is an example of Type II hypersensitivity reaction, also known as cytotoxic hypersensitivity. In this reaction, antibodies bind to specific antigens on the surface of cells, marking them for destruction by complement or other immune cells. In the case of myasthenia gravis, the antibodies against the AChR lead to the destruction of the receptor, reducing the amount of acetylcholine that can bind and trigger muscle contraction.

**Why Each Wrong Option is Incorrect**
* **Option A:** This is incorrect because myasthenia gravis is not an example of a Type I hypersensitivity reaction, which involves IgE antibodies and the release of histamine from mast cells.
* **Option B:** This is incorrect because myasthenia gravis is not an example of a Type III hypersensitivity reaction, which involves the formation of antigen-antibody complexes that deposit in tissues and cause inflammation.
* **Option C:** This is incorrect because myasthenia gravis is not an example of a Type IV hypersensitivity reaction, which involves T-cell mediated responses and is typically seen in delayed hypersensitivity reactions.

**Clinical Pearl / High-Yield Fact**
The thymus gland is often involved in myasthenia gravis, with up to 70% of patients having thymic hyperplasia or thymoma. This is because the thymus is thought to play a role in the development and selection of autoreactive T-cells.

**Correct Answer:** B. Type II hypersensitivity.