Given an entity as input, output another entity which is part of the input entity. These are entities of meronym. In linguistics, meronymy is a semantic relation between a meronym denoting a part and a holonym denoting a whole. In simpler terms, a meronym (i.e., output entity) is in a part-of relationship with its holonym (i.e., input entity).

Q: ecosystem

A: carbon
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Q: cysteine

A: sulfur
****
Q: coil tubule

A:
duct
****