Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
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Question: The heterotroph eats only or mainly plants.

Answer: The heterotroph eats only or mainly what?

Question: Producing sperm and secreting testosterone are the main functions of male reproductive system system.

Answer: Producing sperm and secreting testosterone are the main functions of what system?

Question: Methyl groups are found within amino acids.

Answer:
Methyl groups are found within what?