Flukes and tapeworms:

Options

A. show cephalization
B. have well-developed reproductive systems
C. have well-developed nervous systems
D. have a tube-within-a-tube body plan

Explanation

To solve the question regarding flukes and tapeworms, we will analyze the characteristics of these organisms and their classification.

### Step-by-Step Solution:

1. **Identify the Organisms**: Flukes and tapeworms are both types of flatworms. They belong to the phylum Platyhelminthes.

2. **Understand the Classification**: The phylum Platyhelminthes is characterized by certain features, including their body structure, reproductive system, and nervous system.

3. **Evaluate the Options**:
- **Sequelization**: This term is not typically associated with the characteristics of flukes and tapeworms.
- **Developed Reproductive System**: Flukes and tapeworms have well-developed reproductive systems, which is a significant characteristic of this phylum.
- **Nervous System**: While they do have a nervous system, it is not as complex as in higher organisms.
- **Tube Within Tube Body Plan**: This refers to a body plan seen in more complex organisms, not in flatworms.

4. **Select the Correct Option**: Given the analysis, the correct option is that flukes and tapeworms have a well-developed reproductive system.

### Final Answer:
The correct option is **B: Reproductive system has developed**.

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