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

### Step-by-Step Solution:

1. **Understanding Competition**:
- Competition occurs when two or more organisms vie for the same resource, which can be food, space, or other necessities for survival.
- It is most intense when the competing species are similar in their ecological needs.

2. **Identifying the Context**:
- The question asks about the type of competition that is most fierce.
- We need to consider the relationship between species and their environments.

3. **Analyzing the Options**:
- **Option A**: Unrelated species in the same environment.
- Unrelated species, such as sheep and crows, do not compete for the same resources because they have different ecological niches.
- Therefore, this option is incorrect.

- **Option B**: Two or more closely related species in the same environment.
- Closely related species, like sheep and cattle, often compete for similar resources (like grass) in the same environment.
- This option is likely correct as it represents a scenario of fierce competition.

- **Option C**: Two or more closely related species in different environments.
- If species are in different environments, they do not compete for the same resources, leading to less competition.
- Hence, this option is incorrect.

- **Option D**: Two or more unrelated species in different environments.
- Similar to option A, unrelated species in different environments do not compete for resources.
- This option is also incorrect.

4. **Conclusion**:
- The correct answer is **Option B**: Two or more closely related species in the same environment.