Choose the correct option for flatworms -

Options

A. Flame cells are excretory organ and osmoregulatory
B. Mostly endoparasites
C. Bisexual, internal fertilization, many larval stage
D. All

Answer

To solve the question regarding flatworms, we need to analyze each of the provided options carefully.

### Step-by-Step Solution:

1. **Understanding Flatworms**: Flatworms belong to the phylum Platyhelminthes. They are characterized by being unsegmented, bilaterally symmetrical, and lacking a coelomic cavity.

2. **Evaluating Option A**:
- "Flame cells are their excretory organs and are osmoregulatory."
- This statement is correct. Flame cells are indeed the excretory organs in flatworms, functioning in osmoregulation.

3. **Evaluating Option B**:
- "They are mostly endoparasites."
- This statement is also correct. Many flatworms, such as tapeworms and flukes, are endoparasites, meaning they live inside the host's body.

4. **Evaluating Option C**:
- "They are bisexual, have internal fertilization, and have a larval stage."
- This statement is correct as well. Flatworms are typically hermaphroditic (bisexual), engage in internal fertilization, and many species have a larval stage.

5. **Evaluating Option D**:
- "All means all are correct."
- Since options A, B, and C are all correct, this option is also correct.

### Conclusion:
The correct answer is **Option D: All are correct**.

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