Which of the following is a defining characteristic of living organisms?

Options

A. Growth
B. Reproduction
C. Response to external stimuli
D. Ability to make sound

Explanation

To determine the defining characteristic of living organisms from the given options, we will analyze each option step by step:

### Step 1: Analyze the option "Growth"
- **Explanation**: Growth is often associated with living organisms, but it can also be observed in non-living things. For example, crystals grow as molecules accumulate on their surfaces. This indicates that growth alone is not a definitive characteristic of living organisms.
- **Conclusion**: Growth is not a defining characteristic of living organisms.

### Step 2: Analyze the option "Reproduction"
- **Explanation**: While reproduction is a common feature of many living organisms, not all organisms can reproduce. For instance, sterile humans are living beings but cannot reproduce. This suggests that reproduction cannot be considered a defining characteristic of all living organisms.
- **Conclusion**: Reproduction is not a defining characteristic of living organisms.

### Step 3: Analyze the option "Response to external stimuli"
- **Explanation**: Living organisms respond to external stimuli through their senses. This involves processing information through the nervous system and exhibiting behavior in response to stimuli. This characteristic is universally observed in living organisms, making it a strong candidate for a defining characteristic.
- **Conclusion**: Response to external stimuli is a defining characteristic of living organisms.

### Step 4: Analyze the option "Ability to make sound"
- **Explanation**: Not all living organisms can produce sound. For example, jellyfish, which are living organisms, do not have the capability to make sound due to their lack of a brain. Therefore, the ability to make sound cannot be considered a defining characteristic of living organisms.
- **Conclusion**: The ability to make sound is not a defining characteristic of living organisms.

### Final Answer
Based on the analysis, the defining characteristic of living organisms among the given options is **"Response to external stimuli."**

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