Secondary sexual characteristics are characteristics that help distinguish between males and females. Which of the following characteristics is observed only in boys at the time of puberty?

Options

A. Increase in height
B. Growth of hair in underarms
C. Increase in the size of larynx
D. Growth of hair in the pubic area

Answer

To determine which secondary sexual characteristic is observed only in boys during puberty, we can analyze the provided options step by step.

### Step-by-Step Solution:

1. **Understanding Secondary Sexual Characteristics**:
- Secondary sexual characteristics are features that develop during puberty and help distinguish males from females.

2. **Analyzing Option 1: Increase in Height**:
- While boys generally experience a growth spurt during puberty, this characteristic is not exclusive to boys. Girls also grow taller during puberty.
- **Conclusion**: This option is incorrect.

3. **Analyzing Option 2: Growth of Hair in Underarms**:
- Both boys and girls develop underarm hair during puberty. This characteristic is not exclusive to boys.
- **Conclusion**: This option is incorrect.

4. **Analyzing Option 3: Increase in the Size of Larynx**:
- The larynx, or voice box, grows larger in boys during puberty, leading to a deeper voice. This change is specific to boys and is a defining characteristic of male puberty.
- **Conclusion**: This option is correct.

5. **Analyzing Option 4: Growth of Hair in the Pubic Area**:
- Similar to underarm hair, both boys and girls develop pubic hair during puberty. This characteristic is not exclusive to boys.
- **Conclusion**: This option is incorrect.

### Final Answer:
The characteristic observed only in boys at the time of puberty is the **increase in the size of the larynx** (Option 3).

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