Assertion: Darwin's finches of Galapagos islands have different types of modified beaks according to their food habits.
Reason: Adaptive radiation, leads to development of different functional structure from a common ancestral form.

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that Darwin's finches of the Galapagos Islands have different types of modified beaks according to their food habits. This is true as Darwin observed that these finches adapted to various food sources available on the islands.

**Hint**: Think about how different types of food might require different adaptations in beak structure.

2. **Understanding the Reason**: The reason given is that adaptive radiation leads to the development of different functional structures from a common ancestral form. This is also true, as adaptive radiation explains how species evolve to adapt to different environments and niches from a common ancestor.

**Hint**: Consider how a single species can evolve into multiple forms when exposed to different environmental pressures.

3. **Connecting Assertion and Reason**: The assertion and reason are connected because the different beak types of Darwin's finches are a direct result of adaptive radiation. The finches evolved from a common ancestor to adapt to the diverse food sources available in their environment.

**Hint**: Reflect on how environmental factors can influence the evolution of species.

4. **Conclusion**: Both the assertion and the reason are true and are related to each other. Therefore, the correct answer is that both statements are true and the reason correctly explains the assertion.

**Hint**: Look for relationships between statements to determine if they support each other.

### Final Answer:
Both the assertion and the reason are true, and the reason correctly explains the assertion.