The reason for biological development -

Options

A. Customization of generation
B. Variation in living beings due to environmental
C. Struggle for survival
D. Fossil

Explanation

**Step-by-Step Solution:**

1. **Understanding Biological Development:**
Biological development refers to the changes and advancements that occur in living organisms over time. This can include physical changes, adaptations, and the evolution of new traits.

2. **Analyzing the Options:**
The question presents several options regarding the reasons for biological development. We need to evaluate each one to determine which is the most accurate.

3. **Option 1: Customization of Generation**
- This option suggests that biological development can be customized. However, biological development is primarily governed by genetic factors, and customization is not a viable reason for biological development.

4. **Option 2: Variations in Living Beings Due to Environment**
- While environmental variations can lead to evolution, they do not directly account for biological development. Evolution involves changes over long periods and is not solely responsible for the immediate developmental processes in organisms.

5. **Option 3: Struggle for Survival**
- This option refers to the challenges organisms face in their environment, which leads to adaptations. The struggle for survival drives the enhancement of bodily features and the development of new characteristics. For example, humans have developed advanced speech capabilities over time due to the need for communication.

6. **Option 4: Fossils Show Past Life**
- Fossils provide insights into the history of life on Earth but do not directly explain the reasons for biological development. They are more of a record of past organisms rather than a cause of development.

7. **Conclusion:**
- After evaluating all options, the most accurate reason for biological development is the "struggle for survival." This struggle leads to adaptations and the development of new traits that help organisms thrive in their environments.

**Final Answer:**
The reason for biological development is the struggle for survival, which drives adaptations and the enhancement of traits in organisms.

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