Select the mismatch.

Options

A. Benign tumours Possess contact inhibition
B. Secondary lymphoid organ - Tonsil.
C. Autoimmune disease - Myasthenia gravis.
D. Vaccination - Active immunity

Answer

To solve the question of selecting the mismatch from the given options, we need to analyze each statement one by one:

1. **Benign tumors possess contact inhibition**:
- Contact inhibition is a process where normal cells stop growing when they come into contact with each other. Benign tumors, while they are not cancerous and do not spread, do not exhibit contact inhibition. Therefore, this statement is **incorrect**.

2. **Secondary lymphoid organ, tonsil**:
- Tonsils are indeed classified as secondary lymphoid organs. They play a role in the immune response. This statement is **correct**.

3. **Autoimmune disease, myasthenia gravis**:
- Myasthenia gravis is an autoimmune disease where the immune system attacks the body's own tissues, specifically affecting communication between nerves and muscles. This statement is **correct**.

4. **Vaccination, active immunity**:
- Vaccination is a method to induce active immunity by exposing the immune system to antigens, prompting it to produce antibodies. This statement is **correct**.

Based on the analysis, the mismatch is the first statement: **"Benign tumors possess contact inhibition."**

### Summary of the Solution:
- The mismatch is **"Benign tumors possess contact inhibition."** This statement is incorrect because benign tumors do not exhibit contact inhibition, which is a characteristic of normal healthy cells.