Characteristic of birds is :-

Options

A. Unisexual and sexual dimorphism absent
B. Bisexual and sexual dimorphism absent
C. Unisexual and sexual dimorphism present
D. Bisexual and sexual dimorphism present

Answer

To answer the question about the characteristics of birds, we will analyze the options provided and determine which one is correct.

### Step-by-Step Solution:

1. **Understanding the Options**: The question provides four options regarding the characteristics of birds, specifically focusing on their reproductive systems and sexual dimorphism.

2. **Evaluating Option 1**: The first option states "unisexual and sexual dimorphism absent".
- **Analysis**: Birds are not unisexual; they typically have distinct male and female individuals. Therefore, this option is incorrect.

3. **Evaluating Option 2**: The second option states "bisexual and sexual dimorphism absent".
- **Analysis**: While some birds may have both male and female reproductive organs in the same individual (bisexual), most bird species exhibit sexual dimorphism, where males and females have different physical characteristics. Thus, this option is also incorrect.

4. **Evaluating Option 3**: The third option states "unisexual and sexual dimorphism present".
- **Analysis**: This option correctly identifies that birds are generally unisexual (with separate male and female individuals) and exhibit sexual dimorphism (where males and females have different appearances). For example, in parrots, males may have distinct markings that females do not. This option is correct.

5. **Evaluating Option 4**: The fourth option states "bisexual and sexual dimorphism present".
- **Analysis**: While sexual dimorphism is present in birds, this option incorrectly states that birds are bisexual. Therefore, this option is also incorrect.

### Conclusion:
The correct answer is **Option 3: Unisexual and sexual dimorphism present**.

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