For an ecosystem, the two main structural features are-
(i) species composition
(ii) Energy flow
(iii) Decomposition
(iv) Stratification

Options

A. I and iv only
B. ii and iii only
C. i only
D. ii , iii and iv only

Answer

To solve the question regarding the two main structural features of an ecosystem, we will analyze each of the given options step by step.

### Step 1: Identify the Options
The options provided are:
1. Species Composition
2. Energy Flow
3. Decomposition
4. Stratification

### Step 2: Analyze Each Option
- **Species Composition**: This refers to the variety and abundance of different species present in a community. It is a fundamental structural feature of an ecosystem because it determines the interactions among organisms and their roles in the ecosystem. **(Correct)**

- **Energy Flow**: While energy flow is crucial for understanding how energy moves through an ecosystem (from producers to consumers to decomposers), it is not considered a structural feature. It describes the functional aspect of an ecosystem rather than its structure. **(Incorrect)**

- **Decomposition**: This is a process that recycles nutrients back into the ecosystem but does not describe a structural feature. It is more about the functional dynamics of an ecosystem. **(Incorrect)**

- **Stratification**: This refers to the vertical layering of different habitats within an ecosystem, such as layers in a forest (canopy, understory, forest floor). It is a structural feature as it describes the physical arrangement of different layers in a habitat. **(Correct)**

### Step 3: Conclusion
Based on the analysis, the two main structural features of an ecosystem are:
1. Species Composition
2. Stratification

### Final Answer
The correct answer is **Species Composition and Stratification**.