Animals of colder climates generally have smaller limbs. This is called :

Options

A. Niche rule
B. Allen's rule
C. Ehrilch rule
D. None of these

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the phenomenon where animals in colder climates tend to have smaller limbs.

2. **Reviewing the Options**: The options provided are:
- A) Nietzsche's rule
- B) Allen's rule
- C) Ehrlich's rule
- D) None of these

3. **Analyzing Nietzsche's Rule**:
- Nietzsche's rule is related to the competitive exclusion principle, which states that two species cannot occupy the same niche simultaneously due to competition for resources. This rule does not pertain to limb size in animals of colder climates.

4. **Analyzing Allen's Rule**:
- Allen's rule states that animals in colder climates tend to have shorter and thicker limbs compared to those in warmer climates. This adaptation helps to minimize heat loss. Therefore, this option is relevant to the question.

5. **Analyzing Ehrlich's Rule**:
- Ehrlich's rule is not related to limb size or climate; it discusses the consequences of overpopulation. Thus, this option is incorrect.

6. **Evaluating the Last Option**:
- The last option, "None of these," is also incorrect because we have identified Allen's rule as the correct explanation for the phenomenon described in the question.

7. **Conclusion**: Based on the analysis, the correct answer is **B) Allen's rule**.