This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: parasitology, Subject name: Microbiology
[{'content': 'Which of the following show regressive metamorphosis - \nSelect and explain. \nA. Hydatid cyst, B. Cysticercoid, C. Cysticercus bovis, D. Cysticercus cellulosae', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Retrogressive metamorphosis is when an organism changes from a more advanced form to a primitive one.the ruptured hydatid cyst releases protoscolices into tissues which do not develop into adult forms according to law of migration of cestodes.... but they form a new hydatid tissue against the law.... this is called regressive metamorphosis.', 'role': 'assistant'}]