A: The cells that produce and secrete fibres are called fibroblasts.
R: Fibroblasts are the characteristic cells of all types of connective tissue.

Options

A. If both Assertion & Reason are true, and the reason is the correct explanation of the assertion.
B. If both Assertion & Reason are true, but the reason is not the correct explanation of the assertion.
C. If the Assertion is a true statement, but Reason is false.
D. If both Assertion and Reason are false statements.

Answer

To solve the question, we need to analyze the two statements:

**Assertion (A)**: The cells that produce and secrete fibers are called fibroblasts.
**Reason (R)**: Fibroblasts are the characteristic cells of all types of connective tissue.

### Step-by-Step Solution:

1. **Evaluate the Assertion (A)**:
- The assertion states that fibroblasts are the cells responsible for producing and secreting fibers. This is a true statement. Fibroblasts are indeed the cells that synthesize the extracellular matrix and collagen, which are essential components of connective tissue.

2. **Evaluate the Reason (R)**:
- The reason states that fibroblasts are characteristic cells of all types of connective tissue. This statement is partially true. While fibroblasts are present in many types of connective tissue, they are not found in all types. For example, blood is a type of connective tissue that does not contain fibroblasts or fibers in its liquid form.

3. **Determine the Relationship Between A and R**:
- Since the assertion is true but the reason is not true for all types of connective tissue (as blood lacks fibroblasts), the reason does not correctly explain the assertion.

4. **Choose the Correct Option**:
- Based on the evaluations, we conclude that the assertion is true and the reason is false. Therefore, the correct option is option 3: "Assertion is true, but reason is false."

### Final Answer:
The correct answer is option 3: Assertion is true, but reason is false.

---