The correct option is
D Platyhelminthes
Tapeworm belongs to Platyhelminthes.
This is can be confirmed by seeing the general characteristics of Platyhelminthes:
1. They are dorsoventrally flattened.
2. Their bodies are bilaterally symmetrical.
3. They are acoelomate and soft
4. They are tripblastic animals.
So the correct answer is 'Platyhelminthes'.