Competition is most fierce between

Options

A. unrelated species in the same environment .
B. two or more closely related species in the same environment .
C. two or more closely related species in the different environment .
D. none of the above

Answer

To solve the question "Competition is most fierce between," we need to analyze the options provided and determine which scenario leads to the most intense competition among species.

### Step-by-Step Solution:

1. **Understand the Concept of Competition**:
- Competition occurs when two or more species vie for the same resources, such as food, space, or mates. The fierceness of competition is influenced by the similarity of the species and the availability of resources.

2. **Evaluate Option A**:
- **Unrelated species in the same environment**:
- Unrelated species typically have different ecological niches and may not compete for the same resources. Therefore, competition is likely to be less fierce.

3. **Evaluate Option B**:
- **Two or more closely related species in the same environment**:
- Closely related species often have similar ecological needs and may compete for the same resources (like food and habitat). Since they share the same environment and resource requirements, competition is likely to be very intense.

4. **Evaluate Option C**:
- **Two or more closely related species in different environments**:
- In this case, even though the species are closely related, they are in different environments. This means they are not competing for the same resources, leading to less fierce competition.

5. **Evaluate Option D**:
- **None of the above**:
- Since we have identified that option B is a strong candidate for the most intense competition, this option is not applicable.

6. **Conclusion**:
- After evaluating all the options, the most fierce competition occurs between **two or more closely related species in the same environment**. Therefore, the correct answer is **Option B**.

### Final Answer:
**Option B: Two or more closely related species in the same environment.**